The immunogenicity and efficacy of influenza vaccination is markedly lower in the elderly. between GrzB response and hemagglutination inhibition (HAI) titers indicating no relationship between the cytolytic activity and humoral antibody levels in this cohort. Additionally a significant unfavorable correlation between GrzB response and age was observed. These results reveal a reduction in influenza-specific GrzB response as one ages. In conclusion we have developed and optimized an influenza-specific ELISPOT assay for use with frozen cells to quantify the CTL-specific serine protease GrzB as a measure of cellular immunity after influenza vaccination. filtrate Sigma-Aldrich St. Louis MO) as previously reported [20]. Serial two-fold dilutions of the pretreated and inactivated sera (25 μl) were mixed with 4 HA models/25 μl of influenza computer virus and incubated for 30 min at room temperature to allow antigen-antibody binding. An equal volume (50 μl) of 0.5% turkey red blood cell suspension was then added to the mixture. HAI titers were decided after a 45-minute incubation on ice as the reciprocal of the highest serum dilution that completely inhibits hemagglutination [18-20]. 2.5 Granzyme B ELISPOT Assay Influenza-specific GrzB-positive cells were quantified in PBMC cultures using the BDTM Human Granzyme B ELISPOT kit (BD Biosciences San Jose CA) following the manufacturer’s protocol and as previously described [22]. Briefly 96 ELISPOT PVDF microplates were pre-coated with 5 μg/mL capture anti-GrzB antibody in sterile PBS pH 7.2 incubated overnight at 4°C and blocked (two hours at room heat) with RPMI medium containing 10% FCS. Cryopreserved PBMCs were thawed counted Casp3 and plated in ELISPOT plates at 2×105 cells/well in RPMI medium made up of 5% FCS as previously reported [17]. Cells were mock-stimulated with RPMI 5% FCS (unstimulated wells in triplicate) or stimulated with influenza A/California/7/2009/H1N1-like computer virus at a multiplicity of contamination/MOI of 0.5 for 24 hours incubation at 37?鉉 in 5 % CO2 (stimulated wells in triplicate). The optimal assay parameters were chosen based on screening three incubation periods after activation (18 h 20 h and 24 h) and three different MOIs GAP-134 (Danegaptide) (0.1 0.2 and 0.5). With an MOI of 0.5 (24 h incubation) we achieved significantly higher influenza-specific GrzB response compared to lower MOIs in eight optimization samples (p<0.05 data GAP-134 (Danegaptide) not shown). Phytohemagglutinin/PHA (5 μg/mL Sigma St. Louis MO) was used as a subject-specific positive control. After the incubation period ELISPOT plates were processed following the manufacturer’s specifications using a biotinylated anti-GrzB antibody as a secondary antibody (2 μg/mL final concentration) streptavidin-horseradish peroxidase/HRP (dilution 1:100) and a tetramethylbenzidine (TMB)-H peroxidase substrate (Moss Inc. Pasadena MD) for assay development (20 min. at room heat) as previously reported [15 17 All assay plates were scanned and analyzed using the same pre-optimized counting parameters (including sensitivity spot size background and spot separation) on an ImmunoSpot? S6Macro696 Analyzer (Cellular Technology Ltd. Cleveland GAP-134 (Danegaptide) OH) using ImmunoSpot? version 5.1 software (Cellular Technology Ltd.). Quality control was performed by a single operator to eliminate spurious results [15 17 The results are offered as spot-forming counts GAP-134 (Danegaptide) (SFCs) per 2×105 cells as subjects’ medians (median of influenza virus-specific stimulated response minus the median unstimulated response). The same assay parameters and reagents (including viral strain for activation) kits scanning and counting parameters and QC metrics were utilized for all subjects. 2.6 Statistical Methods Influenza H1N1-specific GrzB response is calculated as the median of triplicate stimulated cells minus the median of triplicate unstimulated cells. Results are offered as percentiles of the distribution box and whisker plots at each visit and scatter plots by age. Differences in H1N1-specific GrzB response between visits were assessed using the Wilcoxon signed rank test. Correlation between H1N1-specific GrzB response and age was evaluated using Spearman’s method. Intra-class correlation was assessed overall and by visit for the triplicate stimulated using Shrout and Fleiss’s method [23]. Analyses were conducted using the R statistical language software package version 2.15 and SAS? version 9.3 [24]. 3.