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During inflammation, neutrophils are rapidly mobilized from the bone marrow storage pool into peripheral blood (PB) to enter lesional sites, where most rapidly undergo apoptosis. Monocytes constitute a second wave of inflammatory immigrates, giving rise to long-lived macrophages and dendritic cell subsets. According to descriptive immunophenotypic and cell culture studies, neutrophils may directly "transdifferentiate" into monocytes/macrophages. We provide mechanistic data in human and murine models supporting the existence of this cellular pathway. First, the inflammatory signal-induced MKK6-p38MAPK cascade activates a monocyte differentiation program in human granulocyte colony-stimulating factor-dependent neutrophils. Second, adoptively transferred neutrophils isolated from G-CSF-pretreated mice rapidly acquired monocyte characteristics in response to inflammatory signals in vivo. Consistently, inflammatory signals led to the recruitment of osteoclast progenitor cell potential from ex vivo-isolated G-CSF-mobilized human blood neutrophils. Monocytic cell differentiation potential was retained in left-shifted band-stage neutrophils but lost in neutrophils from steady-state PB. MKK6-p38MAPK signaling in HL60 model cells led to diminishment of the transcription factor C/EBPα, which enabled the induction of a monocytic cell differentiation program. Gene profiling confirmed lineage conversion from band-stage neutrophils to monocytic cells. Therefore, inflammatory signals relayed by the MKK6-p38MAPK cascade induce monocytic cell differentiation from band-stage neutrophils., (© 2014 by The American Society of Hematology.)

Histone deacetylase 1 and 2 (HDAC1/2) regulate chromatin structure as the catalytic core of the Sin3A, NuRD and CoREST co-repressor complexes. To better understand the key pathways regulated by HDAC1/2 in the adaptive immune system and inform their exploitation as drug targets, we have generated mice with a T-cell specific deletion. Loss of either HDAC1 or HDAC2 alone has little effect, while dual inactivation results in a 5-fold reduction in thymocyte cellularity, accompanied by developmental arrest at the double-negative to double-positive transition. Transcriptome analysis revealed 892 misregulated genes in Hdac1/2 knock-out thymocytes, including down-regulation of LAT, Themis and Itk, key components of the T-cell receptor (TCR) signaling pathway. Down-regulation of these genes suggests a model in which HDAC1/2 deficiency results in defective propagation of TCR signaling, thus blocking development. Furthermore, mice with reduced HDAC1/2 activity (Hdac1 deleted and a single Hdac2 allele) develop a lethal pathology by 3-months of age, caused by neoplastic transformation of immature T cells in the thymus. Tumor cells become aneuploid, express increased levels of c-Myc and show elevated levels of the DNA damage marker, γH2AX. These data demonstrate a crucial role for HDAC1/2 in T-cell development and the maintenance of genomic stability.

Cytokines are deregulated in cancers and can contribute to tumor growth. In patients with diffuse large-cell lymphoma (DLBCL), we observed higher levels of JAK/STAT pathway-related serum cytokines (ie, IL-6, IL-10, epidermal growth factor, and IL-2) compared with controls. Of these, only IL-10 activated the JAK2 pathway in lymphoma cells in vitro. Patients with high serum IL-10 had shorter event-free survival (EFS) than patients with low levels (P > .01) and high IL-10 was correlated with high lactase dehydrogenase (P = .0085) and higher International Prognostic Index scores (P = .01). To explore the mechanism by which IL-10 may contribute to an inferior EFS, we investigated the effect of IL-10 on the JAK2 pathway and found that the IL-10/IL-10 receptor complex up-regulated JAK2 signaling. Neutralizing Ab to IL-10 inhibited constitutive and IL-10-induced JAK2/STAT3 phosphorylation. JAK2 inhibition dephosphorylated JAK2 and STAT3 and caused an inhibitory effect on phospho-JAK2-positive DLBCL cells; there was a minimal effect on phospho-JAK2-negative cells. Apoptosis induced by JAK2 inhibition was dependent on inhibition of autocrine IL-10 and c-myc expression and independent of Bcl-2 family expression. These results provide the rationale for testing JAK2 inhibitors in DLBCL patients, and indicate that serum IL-10 may be a biomarker to identify patients more likely to respond to JAK2-targeted therapy.

Stimulation via the T-cell receptor (TCR) activates p38α and p38β by phosphorylation of p38 Tyr-323 (p38(Y323)). Here we characterize knockin mice in which p38α and/or β Tyr-323 has been replaced with Phe. We find that p38α accounts for two-thirds and p38β the remainder of TCR-induced p38 activation. T cells from double knockin mice (p38αβ(Y323F)) had defects in TCR-mediated proliferation and Th1 and Th17 skewing, the former corresponding with an inability to sustain T-bet expression. Introduction of p38α(Y323F) into Gadd45α-deficient mice, in which the alternative p38 pathway is constitutively active, reversed T-cell hyperproliferation and autoimmunity. Furthermore, p38αβ(Y323F) mice had delayed onset and reduced severity of the inflammatory autoimmune diseases collagen-induced arthritis and experimental autoimmune encephalomyelitis. Thus, T cell-specific alternative activation of p38 is an important pathway in T-cell proliferation, Th skewing, and inflammatory autoimmunity, and may be an attractive tissue-specific target for intervention in these processes.

In chronic disorders related to endothelial cell dysfunction, plasma β₂ glycoprotein I (β₂GPI) plays a role as a target antigen of pathogenetic autoimmune responses. However, information is still lacking to clarify why β₂GPI triggers autoimmunity. It is possible that posttranslational modification of the protein, such as nonenzymatic glycosylation, leads to the formation of advanced glycation end products (AGEs). The aim of our study was to explore whether glucose-modified β₂GPI is able to interact and activate monocyte-derived immature dendritic cells (iDCs) from healthy human donors. SDS-PAGE and spectrofluorometric analyses indicated that β₂GPI incubated with glucose was sugar modified, and that this modification likely consisted of AGE formation, resulting in AGE-β₂GPI. AGE-β₂GPI caused phenotypical and functional maturation of iDCs involving the activation of p38 MAPK, ERK, and NF-κB. It also induced on DCs a significant up-regulation of RAGE, the receptor for AGEs. Evidence for RAGE involvement comes from blocking experiments with an anti-RAGE mAb, confocal analysis, and coimmunoprecipitation experiments. AGE-β₂GPI-stimulated DCs had increased allostimulatory ability and primed naive T lymphocytes toward a Th2 polarization. These findings might explain in part the interactive role of β₂GPI, AGEs, and DCs in chronic disorders related to endothelial cell dysfunction.

A humanized IgG4 anti-HLA-DR monoclonal antibody (IMMU-114), engineered to avoid side effects associated with complement activation, was examined for binding and cytotoxicity on leukemia, lymphoma, and multiple myeloma cell lines and chronic lymphocytic leukemia (CLL) patient specimens, followed by evaluation of the effects of IMMU-114 on extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) signaling pathways. HLA-DR was expressed on the majority of these cells at markedly higher levels than CD20, CD22, and CD74. IMMU-114 was toxic to mantle cell lymphoma, CLL, acute lymphoblastic leukemia, hairy cell leukemia, non-Hodgkin lymphoma (including rituximab-resistant), and multiple myeloma cell lines, and also patient CLL cells. IMMU-114 induced disease-free survival in tumor-bearing SCID mice with early-stage disease and in models that are relatively resistant to anti-CD20 monoclonal antibodies. Despite positive staining, acute myelogenous leukemic cells were not killed by IMMU-114. The ability of IMMU-114 to induce activation of ERK and JNK signaling correlated with cytotoxicity and differentiates the mechanism of action of IMMU-114 from monoclonal antibodies against CD20 and CD74. Thus, antigen expression is not sufficient for cytotoxicity; antibody-induced hyperactivation of ERK and JNK mitogen activated protein kinase signaling pathways are also required.

The processing of pro-interleukin-1beta depends on activation of caspase-1. Controversy has arisen whether Toll-like receptor (TLR) ligands alone can activate caspase-1 for release of interleukin-1beta (IL-1beta). Here we demonstrate that human blood monocytes release processed IL-1beta after a one-time stimulation with either TLR2 or TLR4 ligands, resulting from constitutively activated caspase-1 and release of endogenous adenosine triphosphate. The constitutive activation of caspase-1 depends on the inflammasome components, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), and NALP3, but in monocytes caspase-1 activation is uncoupled from pathogen-associated molecular pattern recognition. In contrast, macrophages are unable to process and release IL-1beta solely by TLR ligands and require a second adenosine triphosphate stimulation. We conclude that IL-1beta production is differentially regulated in monocytes and macrophages, and this reflects their separate functions in host defense and inflammation.

T cells possess a p38 activation alternative pathway in which stimulation via the antigen receptor (T-cell receptor [TCR]) induces phosphorylation of p38alpha and beta on Tyr323. To assess the contribution of this pathway to normal T-cell function, we generated p38alpha knockin mice in which Tyr323 was replaced with Phe (p38alpha(Y323F)). TCR-mediated stimulation failed to activate p38alpha(Y323F) as measured by phosphorylation of the Thr-Glu-Tyr activation motif and p38alpha catalytic activity. Cell-cycle entry was delayed in TCR-stimulated p38alpha(Y323F) T cells, which also produced less interferon (IFN)-gamma than wild-type T cells in response to TCR-mediated but not TCR-independent stimuli. p38alpha(Y323F) mice immunized with T-helper 1 (Th1)-inducing antigens generated normal Th1 effector cells, but these cells produced less IFN-gamma than wild-type cells when stimulated through the TCR. Thus, the Tyr323-dependent pathway and not the classic mitogen-activated protein (MAP) kinase cascade is the physiologic means of p38alpha activation through the TCR and is necessary for normal Th1 function but not Th1 generation.

Dexamethasone (DM) is a synthetic member of the glucocorticoid (GC) class of hormones that possesses anti-inflammatory and immunosuppressant activity and is commonly used to treat chronic inflammatory disorders, severe allergies, and other disease states. Although GCs are known to mediate well-defined transcriptional effects via GC receptors (GCR), there is increasing evidence that GCs also initiate rapid nongenomic signaling events in a variety of cell types. Here, we report that DM induces the phosphorylation of Lck and the activation of other downstream mediators, including p59Fyn, Zap70, Rac1, and Vav in resting but not activated human T cells. DM treatment also augments CXCL12-mediated signaling in resting T cells through its cell surface receptor, CXCR4 resulting in the enhanced actin polymerization, Rac activation, and cell migration on ligand exposure. Lck was found to be a critical intermediate in these DM-induced signaling activities. Moreover, DM-mediated Lck phosphorylation in T cells was dependent on the presence of both the GCR and the CD45 molecule. Overall, these results elucidate additional nongenomic effects of DM and the GCR on resting human T cells, inducing Lck and downstream kinase activation and augmenting chemokine signaling and function.

Activation of PI3K is among the earliest signaling events observed in T cells after conjugate formation with antigen-presenting cells (APCs). The relevant PI3K catalytic isoform and relative contribution of the TcR and CD28 to PI3K activity at the immune synapse have not been determined unequivocally. Using a quantitative imaging-based assay, we show that the PI3K activity at the T cell-APC contact area is dependent on the p110delta, but not the p110gamma, isoform of PI3K. CD28 enhanced PIP3 production at the T-cell synapse independently of its YMNM PI3K-recruitment motif that instead was required for efficient PKC recruitment. CD28 could partially compensate for the lack of p110delta activity during T-cell activation, which indicates that CD28 and p110delta act in parallel and complementary pathways to activate T cells. Consistent with this, CD28 and p110delta double-deficient mice were severely immune compromised. We therefore suggest that combined pharmaceutic targeting of p110delta activity and CD28 costimulation has potent therapeutic potential.

During T-cell activation, a number of cytokine-activated signaling cascades, including the Jak-STAT, phosphoinositol 3-kinase (PI 3-kinase), and mitogen-activated protein kinase (MAPK) pathways, play important roles in modulating the expression of target genes and mediating a cellular response. We now report that interleukin 2 (IL-2) and IL-15, but not IL-7, rapidly activate the p90 ribosomal S6 kinases, Rsk1 and Rsk2, in human T lymphocytes. Surprisingly, mouse spleen T cells transduced with either the wild-type or a dominant-negative (DN) Rsk2-expressing retrovirus could not be recovered, in contrast to the normal survival of T cells transduced with retroviruses expressing wild-type or DN mutants of Rsk1 or Rsk3. Examination of Rsk2 knockout (KO) mice revealed normal T-cell development, but these T cells had delayed cell-cycle progression and lower production of IL-2 in response to anti-CD3 and anti-CD28 stimulation in vitro. Moreover, Rsk2 KO mice had defective homeostatic T-cell expansion following sublethal irradiation in vivo, which is known to involve T-cell receptor (TCR), IL-2, and/or IL-15 signals, each of which we demonstrate can rapidly and potently activate Rsk2 in mouse T cells. These results indicate an essential nonredundant role of Rsk2 in T-cell activation.

Foreign CpG-DNA from viruses and bacteria can activate memory B cells through binding to toll-like receptor 9, and this pathway has been hypothesized to be involved in the continuous activation of memory B cells ensuring life-long humoral immunity. In this study, we demonstrate that retinoic acid (RA) is a potent coactivator of this pathway in human B cells. RA enhanced the CpG-mediated proliferation of CD27(+) memory B cells, and the proliferative response was accompanied by increased immunoglobulin (Ig) secretion indicative of plasma-cell formation. The RA-induced proliferation was preceded by enhanced expression of cyclin D3, and both the expression of cyclin D3 and the induced Ig secretion were found to be dependent on IL-10. Of importance, RA increased the CpG-induced phosphorylation of ERK1/2, p38MAPK, and IkappaB as early as 30 minutes after stimulation. By using specific inhibitors, all the RA-mediated events, including proliferation, cyclin D3 expression, IL-10 secretion, and Ig secretion, were shown to be dependent on p38MAPK. Hence, we propose that RA can strengthen humoral immunity by promoting CpG-mediated stimulation of CD27(+) B cells via activation of p38MAPK resulting in increased proliferation and differentiation to Ig-secreting plasma cells.

Although typically considered a neurotransmitter, there is substantial evidence that serotonin (5-HT) plays an important role in the pathogenesis of inflammatory disorders. Despite these findings, the precise role of 5-HT in modulating immune function, particularly T-cell function, remains elusive. We report that naive T cells predominantly express the type 7 5-HT receptor (5-HTR), and expression of this protein is substantially enhanced on T-cell activation. In addition, T-cell activation leads to expression of the 5-HT(1B) and 5-HT(2A) receptors. Significantly, exogenous 5-HT induces rapid phosphorylation of extracellular signal-regulated kinase-1 and -2 (ERK1/2) and IkappaBalpha in naive T cells. 5-HT-induced activation of ERK1/2 and NFkappaB is inhibited by preincubation with a specific 5-HT(7) receptor antagonist. Thus, 5-HT signaling via the 5-HT(7) receptor may contribute to early T-cell activation. In turn, 5-HT synthesized by T cells may act as an autocrine factor. Consistent with this hypothesis, we found that inhibition of 5-HT synthesis with parachlorophenylalanine (PCPA) impairs T-cell activation and proliferation. Combined, these data demonstrate a fundamental role for 5-HT as an intrinsic cofactor in T-cell activation and function and suggest an alternative mechanism through which immune function may be regulated by indoleamine 2,3-dioxygenase-mediated catabolism of tryptophan.

MRL/lpr mice develop a human lupuslike syndrome and, as in autoimmune lymphoproliferative syndrome (ALPS), massive lymphoproliferation due to inactivation of Fas-mediated apoptosis. Presently, no effective therapy exists for ALPS, and long term, therapies for lupus are hazardous. We show herein that arsenic trioxide (As2O3) is able to achieve quasi-total regression of antibody- and cell-mediated manifestations in MRL/lpr mice. As2O3 activated caspases and eliminated the activated T lymphocytes responsible for lymphoproliferation and skin, lung, and kidney lesions, leading to significantly prolonged survival rates. This treatment also markedly reduced anti-DNA autoantibody, rheumatoid factor, IL-18, IFN-gamma, nitric oxide metabolite, TNF-alpha, Fas ligand, and IL-10 levels and immune-complex deposits in glomeruli. As2O3 restored cellular reduced glutathione levels, thereby limiting the toxic effect of nitric oxide, which is overproduced in MRL/lpr mice. Furthermore, As2O3 protected young animals against developing the syndrome and induced almost total disease disappearance in older affected mice, thereby demonstrating that it is a novel promising therapeutic agent for autoimmune diseases.

T-cell large granular lymphocytic leukemia (T-LGL) is characterized by chronic clonal lymphoproliferation of cytotoxic T lymphocytes (CTLs). Despite exhibiting phenotypic properties of antigen-activated cells, including expression of Fas and FasL, T-LGL cells accumulate and demonstrate resistance to apoptosis. We propose that increased activity of a prosurvival signaling pathway in T-LGL is responsible for attenuated apoptosis in T-LGL. Given the importance of the phosphatidylinositol-3 kinase (PI3K)-AKT pathway in regulating the balance between survival and apoptosis, we analyzed AKT activity in T-LGL cells. Compared with resting CTLs from healthy donors, patients' T-LGL cells showed higher levels of phosphorylated AKT. We demonstrate that phospho-AKT induction is dependent on the upstream activity of a Src family kinase. Since the PI3K-AKT pathway can antagonize the ability of Fas to initiate apoptosis, we hypothesized that inhibition of PI3K would lead to reacquisition of Fas sensitivity in T-LGL. Inhibition of the PI3K-AKT pathway alone led to brisk spontaneous apoptosis of T-LGL. These results suggest that T-LGL pathogenesis is dependent on activity of the PI3K-AKT pathway, without which the leukemic cells will begin to undergo spontaneous apoptosis. We propose that novel therapeutics inhibiting the PI3K-AKT axis may provide effective treatment for T-LGL.

The blood-brain barrier (BBB) is compromised during progressive HIV-1 infection, but how this occurs is incompletely understood. We studied the integrity of tight junctions (TJs) of brain microvascular endothelial cells (BMVECs) in an in vitro BBB system and in human brain tissues with HIV-1 encephalitis (HIVE). A downregulation of TJ proteins, claudin-5 and occludin, paralleled monocyte migration into the brain during HIVE. Because small G proteins (such as Rho) can play a role in BMVEC TJ assembly, an artificial BBB system explored the relationship among TJs, Rho/Rho kinase (RhoK) activation, and transendothelial monocyte migration. Coculture of monocytes with endothelial cells led to Rho activation and phosphorylation of TJ proteins. Rho and RhoK inhibitors blocked migration of infected and uninfected monocytes. The RhoK inhibitor protected BBB integrity and reversed occludin/claudin-5 phosphorylation associated with monocyte migration. BMVEC transfection with a constitutively active mutant of RhoK led to dislocation of occludin from the membrane and loss of BMVEC cell contacts. When dominant-negative RhoK-transfected BMVECs were used in BBB constructs, monocyte migration was reduced by 84%. Thus, loss of TJ integrity was associated with Rho activation caused by monocyte brain migration, suggesting that Rho/RhoK activation in BMVECs could be an underlying cause of BBB impairment during HIVE.

Thioredoxin truncated at its carboxy terminal (Trx80) acts as a cytokine that stimulates monocytes and eosinophils. In the present study, Trx80 was shown to induce differentiation of human CD14(+) monocytes into a cell type not described previously, which we designate as Trx80-activated monocytes (TAMs). TAMs resemble immature dendritic cells (iDCs) generated in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 4 (IL-4) in that both these cell populations exhibit increased proportions of CD1a(+) and mannose receptor (MR)(+) cells. However, in contrast to iDCs, TAMs express high proportion of CD14 and lower proportion of CD83 and HLA-DR. Functional assays revealed that, in comparison to iDCs, TAMs 1) exhibit a higher pinocytic capacity; 2) release significantly higher amounts of the proinflammatory cytokines tumor necrosis factor-alpha (TNF alpha), IL-1 beta, and IL-6 and of the anti-inflammatory cytokine IL-10; and 3) induce a significantly lower proliferative response in allogeneic peripheral blood mononuclear cells (PBMCs). Indeed, Trx80 appears to be the first endogenous substance shown to have the capacity on its own to induce IL-10 production by monocytes. Analysis of the mitogen-activated protein (MAP) kinase signaling pathway revealed that Trx80 induces phosphorylation of p38, extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK). We propose that Trx80 is an early signal in response to danger, and that TAMs may play a major role in triggering innate immune responses.

On encountering a danger signal, dendritic cells (DCs) undergo a complex maturation process and become specialized in antigen presentation. We previously reported that engagement of major histocompatibility complex (MHC) class II molecules located on immature DCs in membrane rafts by lymphocyte activation gene-3 (LAG-3; CD223) leads to DC maturation. In contrast, exposure of DCs to class II-specific monoclonal antibodies (mAbs) did not lead to maturation. Here, we have investigated the signal transduction pathways involved in the LAG-3-induced maturation of human monocyte-derived DCs. We first show that areas of raft aggregation (both cholesterol rich and CDw78 microdomains) could be visualized using a soluble LAG-3 protein and confocal microscopy. Engagement of class II molecules by both its natural ligand LAG-3 and class II mAb induces rapid protein phosphorylation of phospholipase Cgamma2 (PLCgamma2) and p72syk as well as activation of phosphatidyl inositol 3-kinase/Akt, p42/44 extracellular signal-regulated protein kinase, and p38 mitogen-activated protein kinase pathways. Studies using inhibitors demonstrate that these 3 pathways are all important in inducing the maturation process of LAG-3-stimulated DCs. When class II molecules were ligated with LAG-3 versus specific antibody, differences in the phosphorylation pattern of c-Akt were observed. Thus, MHC class II signaling in DCs involves several pathways that have to be finely regulated to lead to cell activation and maturation.

Activation of the serine/threonine kinase Akt and the regulation of its activation are recognized as critical in controlling proliferative/survival signals via many hematopoietic receptors. In B lymphocytes, the B-cell receptor (BCR)-mediated activation of Akt is attenuated by co-cross-linking of BCR with the inhibitory receptor Fc gamma RIIB1, and the binding of the SH2 domain-containing inositol phosphatase, SHIP, to Fc gamma RIIB1. Because SHIP dephosphorylates phosphatidylinositol 3,4,5-trisphosphate (PIP3) and activation of Akt requires PIP3, the destruction of this phospholipid has been proposed as the mechanism for Akt inhibition. However, upstream kinases that activate Akt, such as PDK1, also require PIP3 for activation. In this report, we addressed whether SHIP inhibits Akt directly at the level of Akt recruitment to the membrane, indirectly through PDK recruitment/phosphorylation of Akt, or both. We generated stable B-cell lines expressing a regulatable, but constitutively membrane-bound Akt that still required PDK-dependent phosphorylation for activation. Several lines of evidence suggested that activation of this membrane-targeted Akt is not inhibited by Fc gamma RIIB1/SHIP and that PDK is not a target for SHIP-mediated inhibition. These data demonstrate that SHIP inhibits Akt primarily through regulation of Akt membrane localization. We also observed during these studies that Fc gamma RIIB1/SHIP does not inhibit p70(S6k) activation, even though several other PIP3-dependent events were down-regulated. Because the enhanced activation of Akt in the absence of SHIP correlates with hyperproliferation in the myeloid lineage, our data have implications for SHIP and Akt-dependent regulation of proliferation in the hematopoietic lineage. (Blood. 2000;96:1449-1456)

The immune system of patients infected with human immunodeficiency virus (HIV) is in a state of chronic activation; however, the nature of HIV-related immune activation is unknown. As normal T-cell activation involves early tyrosine phosphorylation induced by the T-cell antigen receptor-associated src-family protein tyrosine kinase p59(fyn(T)) (Fyn), we examined a potential role for this kinase in HIV-related immune dysfunction. We determined the relative specific kinase activity of Fyn in lysates of peripheral blood mononuclear cells from 47 normal control individuals tested negative for HIV-1 and -2, human T-cell lymphotropic virus Type I, hepatitis B virus (HBV), hepatitis C virus (HCV), and syphilis; 14 asymptomatic HIV-infected patients having near-normal CD4+ T-cell counts (350 to 980 CD4+ cells/microL); 4 patients with symptomatic acquired immunodeficiency syndrome (AIDS) (<30 CD4+ cells/microL); 13 patients having chronic infection with HBV (6 patients) or HCV (7 patients); and 6 patients with systemic lupus erythematosis (SLE). All patients with asymptomatic HIV disease were shown to have a profound increase (mean increase of 19-fold; range threefold to 56-fold increase; p = 1.33 x 10(-9)) in the relative specific kinase activity of Fyn compared to uninfected controls or patients with hepatitis or SLE. In contrast, patients with AIDS had an Fyn-specific kinase activity that was much less affected (mean increase of threefold; range onefold to sevenfold increase; p = 1.30 x 10(-5)). It was further shown that HIV infection affects the Fyn-specific kinase activity in CD8+-enriched cells, suggesting abnormal Fyn activity in both CD8+ as well as CD4+ T lymphocytes. Initial results implicate a role for the CSK protein tyrosine kinase as responsible for the abnormal Fyn kinase activity observed in HIV-infected patients. These data indicate early and chronic activation of Fyn as a unique HIV-related effect that has the potential to be diagnostic for early HIV infection and/or may serve as a prognostic indicator for advancement to full-blown AIDS. More importantly, sustained activation of the protein tyrosine kinase associated with T-cell antigen receptor function may result in, or contribute to, the immunopathogenic effects associated with HIV infection.