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Background Mass cytometry can differentiate more channels than conventional flow cytometry. However, for clinical use, standardization and agreement with well-established methods is paramount. We compared mass cytometry to standard clinical flow cytometry. Methods Mass and flow cytometry were performed in parallel on peripheral blood samples from 25 healthy individuals. Antibody staining was performed on the same samples at the same time, and analyzed for granulocyte, monocyte, lymphocyte, T, B, NK, CD4 and CD8 percentages. Validation parameters included comparison to flow cytometry, inter- and intra-assay precision and establishment of reference intervals. Results There was a positive correlation between mass and flow cytometry for the eight populations studied (R2 between 0.26 and 0.97). Slopes of the best-fit lines varied from 0.50 to 1.21 (fluorescence/mass). No significant differences in variance were found (F-test, P > 0.05). However, paired t-tests were significantly different for four of the eight markers (granulocytes, NK cells, T cells and CD4 cells), resulting in different reference intervals. Signal intensities were correlated for monocytes, lymphocytes, T, CD4 and CD8 cells (R2 = 0.41-0.57). The mass cytometry intra-assay precisions were 0.7-8.5% and inter-assay precisions 1.5-13.8%. Conclusion Mass and flow cytometry evaluations of whole blood for major cell populations correlate with similar precision and signal intensity. However, for clinical use, separate reference interval studies are required. Cell population identification should rely on gating strategies that take advantage of the characteristics offered by each method. © 2019 International Clinical Cytometry Society.

Shellfish allergy affects approximately 2% of the population and can cause immediate hypersensitivity reactions such as urticaria, swelling, difficulty breathing, and, in some cases, anaphylaxis. Tropomyosin is the major shrimp allergen and binds IgE in two-thirds of patients. A total of 38 shrimp-allergic patients and 20 negative control subjects were recruited and evaluated on the basis of history, skin prick testing, specific immunoglobulin E (IgE) levels, and peripheral blood mononuclear cell proliferation in response to shrimp tropomyosin or shrimp tropomyosin-derived peptides. Of the classically allergic patients by history, 59% tested positive for serum shrimp IgE antibodies. Of patients with shrimp-specific IgE in sera, 70% also had significant IgE levels specific for shrimp tropomyosin. Peripheral blood mononuclear cells from classically shrimp-allergic patients proliferated in a dose-dependent manner in response to to tropomyosin. In addition, a T-cell line derived from a shrimp-allergic patient proliferated specifically in response to tropomyosin-derived peptides. These studies suggest a strategy for immunotherapy using a tropomyosin-derived T-cell epitope vaccination.

Cytomegalovirus (CMV) infection is one of the most important infectious complications of transplantation. Monitoring CMV-specific CD8 T cell immunity is useful for predicting active CMV infection and for directing targeted antiviral therapy. In this study, we examined four basic parameters for validation of CMV-specific tetramer staining and peptide stimulation assays that cover five most frequent HLA class I alleles. We also examined the potential use of CMV-specific CD8+T cell numbers and functional and cytolytic responses in two autologous HSCT recipients treated for multiple myeloma. The coefficient of variation (CV %) of the precision within assays was 3.1−24% for HLA-tetramer staining, 2.5−47% for IFN-γ, and 3.4−59.7% for CD107a/b production upon peptide stimulation. The precision between assays was 5−26% for tetramer staining, 4−24% for IFN-γ, and 5−48% for CD107a/b. The limit of detection was 0.1−0.23 cells/μL of blood for tetramer staining, 0−0.23 cell/μL for IFN-γ, and 0.11−0.98 cells/μL for CD107a/b. The assays were linear and specific. The reference interval with 95% confidence level was 0−18 cells/μL for tetramer staining, 0−2 cells/μL for IFN-γ, and 0–3 cells/μL for CD107a/b. Our results provide acceptable measures of test performance for CMV immune competence assays for the characterization of CD8+T cell responses posttransplant measured in the absolute cell count perμL of blood.

Memory T cells exhibit a high degree of heterogeneity in terms of their phenotype and functional characteristics. It has been proposed that the CCR7 chemokine receptor divides memory T cell populations into central memory T cells and effector memory T cells with distinct functions in secondary immune responses. We were interested whether this hypothesis holds true in experiments performed on Ag-specific CD8+ T cells. To identify CCR7+ cells, we engineered a fluorescent ligand for CCR7; results with the new CC chemokine ligand 19 chemotetramer were verified by staining with a CCR7 mAb. Staining with the CC chemokine ligand 19 chemotetramer reveals two subsets within CCR7+ cells: a CCR7int population containing memory cells and a CCR7high population containing naive T cells. Phenotypic analysis of MHC class I/peptide tetramer-positive cells revealed that HLA-A2-restricted CMV-specific CD8 T cells exhibit the lowest percentage of CCR7+ cells (0.5–5%), while HLA-A2-restricted flu- and HLA-B8-restricted EBV-specific CD8 T cells showed the highest (45–70%). Intracellular staining of unstimulated cells revealed that both CCR7int- and CCR7−-specific CD8 T cells exhibit a detectable level of perforin. Both CCR7int and CCR7− Ag-specific CD8+ T cells produced IFN-γ and TNF-α following short-term peptide stimulation. Therefore, our finding that CCR7+CD8+ T cells are able to exert immediate effector functions requires a substantial revision to the central and effector memory hypothesis.

Shellfish allergy is an immune-mediated adverse reaction to allergenic shellfish and is responsible for significant morbidity and mortality. CD4 T cell responses play an important role in the pathophysiological mechanisms of sensitization and in production of IgE.We sought to identify and validate CD4 T cell shrimp tropomyosin-derived epitopes and characterize CD4 T cell responses in subjects with a clinical history of shellfish allergy.Using an in vitro MHC-peptide binding assay, we screened 91 overlapping peptides and identified 28 epitopes with moderate and strong binding capacities; 3 additional peptides were included based on MHC binding prediction score. These peptides were then examined in proliferation and cytokine release assays with T cells from allergic subjects.17 epitopes restricted to DRB(∗)01:01, DRB1(∗)03:01, DRB1(∗)04:01, DRB1(∗)09:01, DQB1(∗)02:01, DQB1(∗)03:02 and DQB1(∗)05:01 alleles were identified and validated by both the MHC binding and the functional assays. Two peptides showed specificities to more than one MHC class II allele. We demonstrated that these peptides exert functional responses in an epitope specific manner, eliciting predominantly IL-6 and IL-13.The identified epitopes are specific to common MHC class II alleles in the general population. Our study provides important data for the design of peptide-based immunotherapy of shrimp-allergic patients.

Black Creek Canal (BCC) virus is a newly identified virus associated with hantavirus pulmonary syndrome (HPS) in the southeastern United States. Nucleotide sequences were determined for the complete S and M and partial L genomic segments of a BCC virus isolate. Phylogenetic analysis indicates that each of the virus segments is unique, and there is no evidence of genetic reassortment having occurred between this and other previously characterized hantaviruses. All hantavirus-seropositive, wild-caught Sigmodon hispidus which were tested by polymerase chain reaction for the presence of BCC virus RNA were found to be positive, consistent with a chronic virus infection. This finding, together with serologic evidence, confirms S. hispidus as the primary rodent reservoir of this virus. Nucleotide sequence analysis of these PCR products indicates that BCC virus is genetically diverse and may pose a public health threat throughout much of the extensive range of this rodent species. Immunoprecipitation analysis demonstrated the presence of G1-, G2-, and N-specific antibodies in sera from BCC virus-infected patients with HPS and naturally infected S. hispidus. Comparison of the patterns of protein immunoprecipitation obtained with human acute- and convalescent-phase sera suggests that G1- and G2-specific antibodies increase relative to N-specific antibodies during the course of infection. The ratio of G1 to N protein immunoprecipitation by rodent or human acute-phase sera allowed differentiation of BCC and Sin Nombre virus infections.

Tetramers of major histocompatibility complex molecules (MHC) are now well-established reagents for the detection of antigen-specific T cells by flow cytometry. MHC tetramers are prepared by mixing enzymatically biotinylated MHC molecules with commercial preparations of streptavidin, usually conjugated to a fluorescent phycobiliprotein such as phycoerythrin (PE) or allophycocyanin (APC). While data obtained with MHC tetramers prepared with small molecule fluorophores has been reported, considerable lot-to-lot variation among conventional streptavidin conjugates to small molecules prevents routine preparation of such reagents. We now report robust preparation of MHC tetramers with small molecule fluorophores, using a recombinant mutant of streptavidin incorporating a carboxy-terminal cysteine in each of the four identical subunits that is conjugated to maleimide derivatives of any of several small molecule fluorophores. These reagents significantly expand the versatility of the MHC tetramer methodology.

CD1d presentation of alpha-galactosyl ceramides to natural killer T cells has been a focal point of the study of regulatory T cells. KRN7000, an alpha-galactosyl ceramide originally generated from structure activity studies of antitumor properties of marine sponge glycolipids, is currently the most commonly used agonist ligand and is used to stain NKT cells. However, this glycolipid suffers from poor solubility and availability. We have developed an alpha-galactosyl ceramide with improved solubility over KRN7000 that effectively stains NKT cells, both mouse and human, and stimulates cytokine release at low concentrations.

Hantavirus pulmonary syndrome (HPS) is a recently recognized viral zoonosis. The first recognized cases were caused by a newly described hantavirus. Sin Nombre virus (previously known as Muerto Canyon virus), isolated from Peromyscus maniculatus (deer mouse). We describe a 33-year-old Floridian man who resided outside the ecologic range of P maniculatus but was found to have serologic evidence of a hantavirus infection during evaluation of azotemia associated with adult respiratory distress syndrome. Small mammal trapping conducted around this patient's residence demonstrated the presence of antihantaviral antibodies in 13% of Sigmodon hispidus [cotton rat). Serologic testing using antigen derived from the Black Creek Canal hantavirus subsequently isolated from this rodent established that this patient was acutely infected with this new pathogenic American hantavirus. HPS is not confined to the geographical distribution of P maniculatus and should be suspected in individuals with febrile respiratory syndromes, perhaps associated with azotemia, throughout the continental United States.

The large (L) RNA segment of Lassa fever virus (LAS) encodes a putative RNA-dependent RNA polymerase (RdRp or L protein). Similar to other arenaviruses, the LAS L protein is encoded on the genome-complementary strand and is predicted to be 2218 amino acids in length (253 kDa). It has an unusually large non-coding region adjacent to its translation start site. The LAS L protein contains six motifs of conserved amino acids that have been found among arenavirus L proteins and core RdRp of other segmented negative-stranded (SNS) viruses (Arena-, Bunya- and Orthomyxoviridae). Phylogenetic analyses of the RdRp of 20 SNS viruses reveals that arenavirus L proteins represent a distinct cluster divided into LAS-lymphocytic choriomeningitis and Tacaribe-Pichinde virus lineages. Monospecific serum against a synthetic peptide corresponding to the most conserved central domain precipitates a 250 kDa product from LAS and lymphocytic choriomeningitis virus-infected cells.