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Antibody-dependent cell-mediated cytotoxicity (ADCC) by natural killer (NK) lymphocytes eliminates cells infected with viruses. Anti-viral ADCC requires three components: (1) antibody; (2) effector lymphocytes with the Fc-IgG receptor CD16A; and (3) viral proteins in infected cell membranes. Fc-afucosylated antibodies bind with greater affinity to CD16A than fucosylated antibodies; individuals' variation in afucosylation contributes to differences in ADCC. Current assays for afucosylated antibodies involve expensive methods. We report an improved bioassay for antibodies that supports ADCC, which encompasses afucosylation. This assay utilizes the externalization of CD107a by NK-92-CD16A cells after antibody recognition. We used anti-CD20 monoclonal antibodies, GA101 WT or glycoengineered (GE), 10% or ~50% afucosylated, and CD20-positive Raji target cells. CD107a increased detection 7-fold compared to flow cytometry to detect Raji-bound antibodies. WT and GE antibody effective concentrations (EC 50 s) for CD107a externalization differed by 20-fold, with afucosylated GA101-GE more detectable. The EC 50 s for CD107a externalization vs. 51 Cr cell death were similar for NK-92-CD16A and blood NK cells. Notably, the % CD107a-positive cells were negatively correlated with dead Raji cells and were nearly undetectable at high NK:Raji ratios required for cytotoxicity. This bioassay is very sensitive and adaptable to assess anti-viral antibodies but unsuitable as a surrogate assay to monitor cell death after ADCC.

Recent advances in next-generation sequencing (NGS) technologies have opened the door to a wellspring of information regarding the composition of the gut microbiota. Leveraging NGS technology, early metagenomic studies revealed that several diseases, such as Alzheimer's disease, Parkinson's disease, autism, and myalgic encephalomyelitis, are characterized by alterations in the diversity of gut-associated microbes. More recently, interest has shifted toward understanding how these microbes impact their host, with a special emphasis on their interactions with the brain. Such interactions typically occur either systemically, through the production of small molecules in the gut that are released into circulation, or through signaling via the vagus nerves which directly connect the enteric nervous system to the central nervous system. Collectively, this system of communication is now commonly referred to as the gut-microbiota-brain axis. While equally important, little attention has focused on the causes of the alterations in the composition of gut microbiota. Although several factors can contribute, mucosal immunity plays a significant role in shaping the microbiota in both healthy individuals and in association with several diseases. The purpose of this review is to provide a brief overview of the components of mucosal immunity that impact the gut microbiota and then discuss how altered immunological conditions may shape the gut microbiota and consequently affect neuroimmune diseases, using a select group of common neuroimmune diseases as examples.

Background: The NK cell line NK-92 and its genetically modified variants are receiving attention as immunotherapies to treat a range of malignancies. However, since NK-92 cells are themselves tumors, they require irradiation prior to transfer and are potentially susceptible to attack by patients' immune systems. Here, we investigated NK-92 cell-mediated serial killing for the effects of gamma-irradiation and ligation of the death receptor Fas (CD95), and NK-92 cell susceptibility to attack by activated primary blood NK cells., Methods: To evaluate serial killing, we used 51 Cr-release assays with low NK-92 effector cell to target Raji, Daudi or K562 tumor cell (E:T) ratios to determine killing frequencies at 2-, 4-, 6-, and 8-h., Results: NK-92 cells were able to kill up to 14 Raji cells per NK-92 cell in 8 h. NK-92 cells retained high cytotoxic activity immediately after irradiation with 10 Gy but the cells surviving irradiation lost > 50% activity 1 day after irradiation. Despite high expression of CD95, NK-92 cells maintained their viability following overnight Fas/CD95-ligation but lost some cytotoxic activity. However, 1 day after irradiation, NK-92 cells were more susceptible to Fas ligation, resulting in decreased cytotoxic activity of the cells surviving irradiation. Irradiated NK-92 cells were also susceptible to killing by both unstimulated and IL-2 activated primary NK cells (LAK). In contrast, non-irradiated NK-92 cells were more resistant to attack by NK and LAK cells., Conclusions: Irradiation is deleterious to both the survival and cytotoxicity mediated by NK-92 cells and renders the NK-92 cells susceptible to Fas-initiated death and death initiated by primary blood NK cells. Therefore, replacement of irradiation as an antiproliferative pretreatment and genetic deletion of Fas and/or NK activation ligands from adoptively transferred cell lines are indicated as new approaches to increase therapeutic efficacy., (© 2022. The Author(s).)

NK cell ADCC supports monoclonal antibody anti-tumor therapies. We investigated serial ADCC and whether it could be predicted by NK phenotypes, including expression of CD16A, CD2 and perforin. CD16A, the NK receptor for antibodies, has AA158 valine or phenylalanine variants with different affinities for IgG. CD2, a costimulatory protein, associates with CD16A and can augment CD16A-signaling. Pore-forming perforin is essential for rapid NK-mediated killing. NK cells were monitored for their ADCC serial killing frequency (KF). KF is the average number of target cells killed per cell by a cytotoxic cell population. KF comparisons were made at 1:4 CD16pos NK effector:target ratios. ADCC was toward Daudi cells labeled with 51 Cr and obinutuzumab anti-CD20 antibody. CD16A genotypes were determined by DNA sequencing. CD2, CD16A, and perforin expression was monitored by flow cytometry. Serial killing KFs varied two-fold among 24 donors and were independent of CD16A genotypes and perforin levels. However, high percentages of CD2pos of the CD16Apos NK cells and high levels of CD16A were associated with high KFs. ROC analysis indicated that the %CD2pos of CD16Apos NK cells can predict KFs. In conclusion, the extent of serial ADCC varies significantly among donors and appears predictable by the CD2posCD16Apos NK phenotype.

Background: Chronic fatigue syndrome (CFS) is an illness of unknown origin that may have familial risks. Low natural killer (NK) lymphocyte activity was proposed as a risk for familial CFS in 1998. Since then, there have been many studies of NK lymphocytes in CFS in general populations but few in familial CFS. Antibody-dependent cell-mediated cytotoxicity (ADCC) by NK lymphocytes helps control viral infections. ADCC is affected by variant CD16A receptors for antibody that are genetically encoded by FCGR3A ., Methods: This report characterizes ADCC effector NK cell numbers, ADCC activities, and FCGR3A variants of five families each with 2-5 CFS patients, their family members without CFS and unrelated controls. The patients met the Fukuda diagnostic criteria. We determined: CD16Apositive blood NK cell counts; EC50s for NK cell recognition of antibody; ADCC lytic capacity; FCGR3A alleles encoding CD16A variants, ROC tests for biomarkers, and synergistic risks., Results: CFS patients and their family members had fewer CD16Apositive NK cells, required more antibody, and had ADCC that was lower than the unrelated controls. CFS family members were predominantly genetically CD16A F/F s for the variant with low affinity for antibodies. ROC tests indicated unsuitability of ADCC as a biomarker for CFS because of the low ADCC of family members without CFS. Familial synergistic risk vs. controls was evident for the combination of CD16Apositive NK cell counts with ADCC capacity., Conclusions: low ADCC may be a risk factor for familial CFS. Furthermore, characterization of familial CFS represents an opportunity to identify pathogenic mechanisms of CFS., Competing Interests: Competing interests The authors lack financial and non-financial competing interests in this study.

Background: The search for a biomarker specific for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) has been long, arduous and, to date, unsuccessful. Researchers need to consider their expenditures on each new candidate biomarker. In a previous study of antibody-dependent cell-mediated cytotoxicity (ADCC) by natural killer lymphocytes, we found lower ADCC for ME/CFS patients vs. unrelated donors but ruled against low ADCC as a biomarker because of similar ADCC for patients vs. their family members without ME/CFS., Objective: We applied inclusion of family members without ME/CFS, from families with multiple CFS patients, as a second non-ME/CFS control group in order to re-examine inflammation in ME/CFS., Method: Total and CD16A-positive 'non-classical' anti-inflammatory monocytes were monitored., Results: Non-classical monocytes were elevated for patients vs. unrelated healthy donors but these differences were insignificant between patients vs. unaffected family members., Conclusions: Inclusion of family members ruled against biomarker considerations for the monocytes characterized. These pilot findings for the non-classical monocytes are novel in the field of ME/CFS. We recommend that occupational therapists advocate and explain to family members without ME/CFS the need for the family members' participation as a second set of controls in pilot studies to rapidly eliminate false biomarkers, optimize patient participation, and save researchers' labor.

Natural killer (NK) lymphocyte ADCC supports anti-viral protection and monoclonal antibody (mAb) anti-tumor therapies. To predict in vivo ADCC therapeutic responses of different individuals, measurement of both ADCC cellular lytic capacity and their NK cellular receptor recognition of antibodies on 'target' cells are needed, using clinically available amounts of blood. Twenty ml of blood provides sufficient peripheral blood mononuclear cells (PBMCs) for the new assay for lytic capacity described here and for an antibody EC 50 assay for Fc-receptor recognition. For the lytic capacity assay, we employed flow cytometry to quantify the CD16A IgG Fc-receptor positive NK effector cells from PBMCs to avoid loss of NKs during isolation. Targets were 51 Cr-labeled Daudi B cells pretreated with excess obinutuzumab type 2 anti-CD20 mAb and washed; remaining free mAb was insufficient to convert B cells in the PBMCs into 'targets'. We calculated: the percentage Daudis killed at a 1:1 ratio of CD16A-positive NK cells to Daudis (CX1:1); lytic slopes; and ADCC 50 lytic units. Among 27 donors, we detected wide ranges in CX1:1 (16-73% targets killed) and in lytic slopes. Slope variations prevented application of lytic units. We recommend CX1:1 to compare individuals' ADCC capacity. CX1:1 was similar for purified NK cells vs. PBMCs and independent of CD16A V & F genotypes and antibody EC 50 s. With high mAb bound onto targets and the high affinity of obinutuzumab Fc for CD16A, CX1:1 measurements discern ADCC lytic capacity rather than antibody recognition. This assay allows ADCC to be quantified without NK cell isolation and avoids distortion associated with lytic units., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Background: Human blood monocytes are known to include subsets defined by the expression of CD14 and CD16 but otherwise are often assumed to be relatively homogeneous. However, we had observed additional heterogeneity that led us to a more extensive examination of monocytes., Methods: Blood samples from 200 healthy adults without known immunological abnormalities were examined by analysis with a hematology analyzer and by flow cytometry (FCM) to determine leukocyte differential counts, to identify subsets and to measure expression of monocyte-associated molecules., Results: The estimated cell counts of monocytes, neutrophils, total lymphocytes, and T cells all varied to a similar extent, that is, ±30-35%. The fractions of monocyte subsets defined by CD14 and CD16 or by CD163 expression also varied among individuals. FCM examinations showed that all the monocyte-associated molecules that were examined varied in expression in this increasing order-CD244, CD4, CD38, CD91, CD11b, toll-like receptor 2 (TLR2), TIA-1, CD14 (on CD14(Br+) cells), CD86, CD80, HLA-DQ, CD33, and HLA-DR., Conclusions: Human blood monocytes are heterogeneous among healthy adults with respect to cell counts, subsets, and the levels of expression of monocyte-associated molecules. An increase in the "non-classical" (CD14(Lo/Neg) /CD16(+) ) monocyte subset or in the expression of CD11b or TLR2 have known diagnostic/prognostic implications. CD244 and CD4 have well-defined functions on lymphocytes but perform unknown activities on monocytes although their expression appears more narrowly controlled. Together, these data suggest that monocytes should be more extensively examined in both clinical and basic contexts., (© 2013 Clinical Cytometry Society.)

Background: This study was designed to improve identification of human blood monocytes by using antibodies to molecules that occur consistently on all stages of monocyte development and differentiation., Methods: We examined blood samples from 200 healthy adults without clinically diagnosed immunological abnormalities by flow cytometry (FCM) with multiple combinations of antibodies and with a hematology analyzer (Beckman LH750)., Results: CD91 (α2 -macroglobulin receptor) was expressed only by monocytes and to a consistent level among subjects [mean median fluorescence intensity (MFI) = 16.2 ± 3.2]. Notably, only 85.7 ± 5.82% of the CD91(+) monocytes expressed high levels of the classical monocyte marker CD14, with some CD91(+) CD16(+) cells having negligible CD14, indicating that substantial FCM under-counts will occur when monocytes are identified by high CD14. CD33 (receptor for sialyl conjugates) was co-expressed with CD91 on monocytes but CD33 expression varied by nearly ten-fold among subjects (mean MFI = 17.4 ± 7.7). In comparison to FCM analyses, the hematology analyzer systematically over-counted monocytes and eosinophils while lymphocyte and neutrophil differential values generally agreed with FCM methods., Conclusions: CD91 is a better marker to identify monocytes than CD14 or CD33. Furthermore, FCM (with anti-CD91) identifies monocytes better than a currently used clinical CBC instrument. Use of anti-CD91 together with anti-CD14 and anti-CD16 supports the identification of the diagnostically significant monocyte populations with variable expression of CD14 and CD16., (Copyright © 2013 Clinical Cytometry Society.)

Pancreatic lipase-related protein 2 (PLRP2) is induced by IL-4 in vitro in cytotoxic T lymphocyte (CTL) clones and CTLs from immunized wild-type (WT) PLRP2(+/+) are more cytotoxic than PLRP2(-/-) CTLs, suggesting to previous investigators that the lipase PLRP2 might support CTL functions. Here, we further evaluate PLRP2 in CTLs. We found that PLRP2 was optimally induced in splenocytes by 3.5 x 10(-8) M IL-4 by day 6 after activation and was restricted to CD8(+) T cells. PLRP2 mRNA was detected inconsistently (and at low levels) after activation in the presence of IL-2. Cytotoxicity in 4 h (51)Cr assays of WT CTLs was approximately 3-fold the activity of PLRP2(-/-) CTLs cultured with IL-4 and, with IL-2, was unexpectedly approximately 2 fold the activity of PLRP2(-/-) CTLs. Thus, PLRP2 gene ablation affected short-term (perforin-dependent) cytotoxicity, even under the IL-2 conditions. Other variables failed to account for the reduced cytotoxicity. Granzyme B levels, activation markers, and CD8(+) T cell frequencies were similar for WT vs. PLRP2(-/-) CTLs (with either cytokine). Addition of rPLRP2 to IL-4 induced PLRP2(-/-) CTLs (or to cytotoxic granule extracts) failed to increase lysis, suggesting that the missing mediator is more than released PLRP2. Cytotoxicity of WT and PLRP2(-/-) CTLs was similar in 2-day tumor survival assays with IL-4, which can be mediated by perforin-independent mechanisms. We conclude that extracellular PLRP2 lipase is unable to directly augment the cytotoxicity that was lost by PLRP2 ablation and that after reevaluation, the question of what is PLRP2's role in CD8 T cells is still unanswered.

IL-4 induces a lipase, pancreatic lipase related protein 2 (PLRP2), in cytotoxic T lymphocytes (CTLs). Because PLRP2 in semen can mediate lipid-dependent toxicity to sperm, we questioned whether CTL-derived PLRP2 could support similar cytotoxicity toward tumor cells. Recombinant PLRP2 was toxic to P815 tumor cells in 48 h when lipid and another protein, colipase, were present. However, PLRP2-positive CTLs (induced with many lots of IL-4) were unable to mediate lipid-dependent cytotoxicity. Notably, CTLs induced with only one lot of IL-4 had lipid-dependent cytotoxicity. The exceptional lot of IL-4 was effective in multiple experiments at inducing lipid-dependent cytotoxicity. The lipid-dependent cytotoxicity it induced was determined to be perforin-independent. CTLs induced with IL-4 that was unable to induce lipid-dependent cytotoxicity had mRNA for PLRP2 but not mRNA for colipase. Therefore, we added exogenous colipase to the CTL assays but still cytotoxicity was unchanged. We conclude (1) that lipid-dependent cytotoxicity, promoted by the lipase PLRP2 and colipase, will kill tumor cells and (2) that more than PLRP2 alone is required for lipid-dependent cytotoxicity mediated by CTLs., ((c) 2009 John Wiley & Sons, Ltd.)

Perforin, a membrane-permeabilizing protein, is important to T cell cytotoxic action. Perforin has potential to damage the T cell in the endoplasmic reticulum (ER), is sequestered in granules, and later is exocytosed to kill cells. In the ER and after exocytosis, calcium and pH favor perforin activity. We found a novel perforin inhibitor associated with cytotoxic T cell granules and termed it Cytotoxic Regulatory Protein 2 (CxRP2). CxRP2 blocked lysis by granule extracts, recombinant perforin and T cells. Its effects lasted for hours. CxRP2 was calcium stable and refractory to inhibitors of granzyme and cathepsin proteases. Through mass spectrometric analysis of active 50-100 kDa proteins, we identified CxRP2 candidates. Protein disulfide isomerase A3 was the strongest candidate but was unavailable for testing; however, protein disulfide isomerase A1 had CxRP2 activity. Our results indicate that protein disulfide isomerases, in the ER or elsewhere, may protect T cells from their own perforin.

It is widely accepted that naïve T cells require two signals, antigen recognition and co-simulation, to become cytotoxic over the course of 3-5days. However, we observed that freshly isolated murine splenocytes without exposure to antigen become cytotoxic within 24h after culture with IL-15. IL-15 is a cytokine that promotes homeostatic proliferation, maintenance and activation of memory T cells. The induced cytotoxicity, measured by anti-CD3 redirected (51)Cr release, represented the combined activity of T cells regardless of their antigen specificity, and proceeded even when CD44(hi) (memory-associated phenotype) CD8(+) T cells were depleted. Cytotoxic capacity was perforin-dependent and occurred without detectable up-regulation of granzyme B or cell division. After induction, the phenotypic markers for the memory subset and for activation remained unchanged from the expression of resting T cells. Our work suggests that T cells may gain cytotoxic potential earlier than currently thought and even without TCR stimulation.

Bortezomib is a proteasome inhibitor that has direct antitumor effects. We and others have previously demonstrated that bortezomib could also sensitize tumor cells to killing via the death ligand, TRAIL. NK cells represent a potent antitumor effector cell. Therefore, we investigated whether bortezomib could sensitize tumor cells to NK cell-mediated killing. Preincubation of tumor cells with bortezomib had no effect on short-term NK cell killing or purified granule killing assays. Using a 24-h lysis assay, increases in tumor killing was only observed using perforin-deficient NK cells, and this increased killing was found to be dependent on both TRAIL and FasL, correlating with an increase in tumor Fas and DR5 expression. Long-term tumor outgrowth assays allowed for the detection of this increased tumor killing by activated NK cells following bortezomib treatment of the tumor. In a tumor purging assay, in which tumor:bone marrow cell mixtures were placed into lethally irradiated mice, only treatment of these mixtures with a combination of NK cells with bortezomib resulted in significant tumor-free survival of the recipients. These results demonstrate that bortezomib treatment can sensitize tumor cells to cellular effector pathways. These results suggest that the combination of proteasome inhibition with immune therapy may result in increased antitumor efficacy.

The purpose of these studies was to determine the minimal requirements to induce granzyme B, cytotoxic granules and perforin-dependent lytic capacity. To our surprise, both IL-2 and IL-15 induced not only proliferation, but also profound granzyme B and lytic capacity from CD8+ T cells in the absence of antigen or TCR-stimulation. Mouse splenocytes were incubated with mouse r-IL-2 or r-IL-15 for three days, tested by anti-CD3 redirected lysis and examined for intracellular granzyme B and for T cell activation markers. With 10(-8) M IL-2 or IL-15, there was excellent lytic activity at 1:1 effector to target ratios mediated by T cells from wild-type but not from perforin-gene-ablated mice, consistent with multiclonal activation. Lower interleukin concentrations induced less lytic activity. Granzyme B was undetectable on day 0, and greatly elevated on day 3 in CD44hi CD8+ T cells as detected by flow cytometry. Cytokines alone elevated the granzyme B as much as concanavalin A combined with the cytokines. Some ex vivo CD8+ T cells were CD122+, as were the cultured granzyme B+ cells, thus both populations had low-affinity receptors for the interleukins. Only some of the activated cells were proliferating as detected by CFSE labeling. When the cytokines were withdrawn, the cells lost lytic activity within 24 h and then within the next 24 h, died. Our results suggest that high concentrations of either IL-2 or IL-15 will activate the lytic capacity and granzyme B expression of many T cells and that antigen recognition is not required.

The purpose of this study was to examine the 100-fold difference in mycoplasma levels in lungs of gamma interferon knockout (IFN-gamma(-/-)) mice compared to those seen with wild-type BALB/c mice at 3 days postinfection. NK cells secreted IFN-gamma; however, their cytotoxic granule extracts failed to kill mycoplasma. We found a conundrum: the clearance of organisms was as effective in NK-depleted IFN-gamma(-/-) animals as in wild-type mice (with both IFN-gamma and NK cells). NK(+) IFN-gamma(-/-) animals had high mycoplasma burdens, but, after NK-like cell depletion, mycoplasma numbers were controlled. Essentially, IFN-gamma was important in animals with NK-like cells and unimportant in animals without NK cells, suggesting that IFN-gamma counters deleterious effects of NK-like cells. Impairment of innate immunity in IFN-gamma(-/-) mice was not due to NK-like cell killing of macrophages. The increased levels of inflammatory cytokines and neutrophils in lung fluids of NK(+) IFN-gamma(-/-) mice were reduced after NK cell depletion. In summary, in the murine model that resembles chronic human disease, innate immunity to mycoplasma requires IFN-gamma when there are NK-like cells and the positive effects of IFN-gamma counteract negative effects of NK-like cells. When imbalanced, NK-like cells promote disease. Thus, it was not the lack of IFN-gamma but the presence of a previously unrecognized NK-like cell-suppressive activity that contributed to the higher mycoplasma numbers. It appears that pulmonary NK cells may contribute to the immunosuppressive environment of the lung, but when needed, these dampening effects can be counterbalanced by IFN-gamma. Furthermore, there may be instances where perturbation of this regulatory balance contributes to the susceptibility to and severity of disease.

Endothelial cell death induced by cytotoxic T cells is a key initiating event in the development of transplant vascular disease (TVD), the leading cause of late solid organ transplant failure. We studied the role of the granzyme B (GrB) pathwaye, which is one of the main mechanisms by which T cells induce apoptosis of allogeneic targets, in the pathogenesis of TVD. Granzyme B, in combination with perforin (pfn), induced apoptosis of cultured endothelial cells. In hearts transplanted into GrB knockout (GrB-KO) mice, there was a similar level of vasculitis as compared to WT mice, indicating that GrB does not affect immune infiltration into allograft arteries. However, there was a significant reduction in luminal narrowing of allograft arteries from GrB-KO mice as compared to WT recipients. These results indicate that GrB plays a role in endothelial cell death in allograft arteries and in the resultant development of TVD.

Dipeptidyl peptidase I (DPPI, cathepsin C) is a lysosomal cysteine protease that can activate zymogens of several different serine proteases by one step or sequential removal of dipeptides from the N-termini of the pro-protease protein substrates. To find DPPI inhibitors more suitable for cellular applications than diazomethyl ketones, we synthesized three types of inhibitors: dipeptide acyloxymethyl ketones, fluoromethyl ketones, and vinyl sulfones (VS). The acyloxymethyl ketones inhibited DPPI slowly and are moderate inhibitors of cellular DPPI. The fluoromethyl ketones were potent, but the inhibited DPPI regained activity quickly. The dipeptide vinyl sulfones were effective inhibitors for DPPI, but they also inhibited cathepsins B, H, and L weakly. The best inhibitor, Ala-Hph-VS-Ph, had a k2/K(I) of 2,000,000M(-1)s(-1). The vinyl sulfones also inhibited intracellular DPPI, and for this application the more stable inhibitors exhibit better potency. We conclude that vinyl sulfones are promising inhibitors to study the intracellular functions of DPPI.

Optimal differentiation of cytotoxic NK cells is important to provide protective innate immunity to patients after bone marrow transplantation. In vitro differentiation of CD56(+)CD3(-) NK cells takes weeks and is supported by several cytokines, including IL-2, IL-7, and IL-15, and thus can be useful for immunotherapy. However, IL-2 therapy is problematic in vivo, and NK cells differentiated in vitro with only IL-7 lack cytotoxicity. We assessed whether human NK cells initially differentiated in vitro from CD34(+)Lin(-) bone marrow cells with IL-7 could acquire cytotoxicity after exposure to additional cytokines and what changes promoted cytotoxicity. The cells cultured with IL-7 already had granzyme B as well as perforin, as previously reported, the proteins of cytotoxic granules. The cells also lacked LFA-1. After 1 wk of secondary culture with either IL-2 or IL-15, but not with IL-12 or IL-18, the IL-7-cultured cells acquired cytotoxicity. IL-2 or IL-15 also induced LFA-1. Ab to the LFA-1 subunits CD11a and CD18 blocked lysis by the NK cells, indicating that the new LFA-1 correlated with, and was essential for, the cytotoxic function of the in vitro generated cells. The LFA-1 also participated in target cell binding by the in vitro differentiated cells. In this study, we demonstrated a new function for IL-15, the induction of LFA-1 in NK progenitor cells, and that IL-15 does more than merely support NK progenitor cell proliferation. The efficacy after only 1 wk of IL-15 administration is a positive practical feature that may apply to human therapy.

The broadly reactive cysteine protease dipeptidyl peptidase I (DPPI, cathepsin C) is thought to activate all progranzymes (zymogens of lymphocyte serine proteases) to form mature granzymes. We synthesized dipeptide 7-amino-4-methylcoumarin (AMC) substrates containing progranzyme activation sequences and showed that they were efficiently hydrolyzed by DPPI. However, DPPI will not hydrolyze Ile-Ile-AMC, the N-terminal dipeptide sequence found in mature granzymes. Introduction of the nonphysiological homophenylalanine (Hph) residue at P1 resulted in the best substrate Ala-Hph-AMC for DPPI (k(cat)/K(m)=9,000,000M(-1)s(-1)). The charged N-terminal amino group of the substrate was essential and replacement of the NH(2) group with OH or NH(CH(3)) in Gly-Phe-AMC reduced the k(cat)/K(m) value by two to three orders of magnitude. A hydrazide azaglycine analog, NH(2)NHCO-Phe-AMC, was not hydrolyzed at pH 5.5, but underwent slow hydrolysis at lower pHs where the amino group is partially protonated. DPPI also failed to hydrolyze NH(2)COCH(2)-Phe-AMC, where the NH(2) group is unprotonated. The results reported in this paper should be useful in the design of better DPPI inhibitors to block granzyme maturation and granzyme-dependent apoptosis.