An association between ABO group and HLA antibody detection.

BACKGROUND: US blood centers can screen female plateletpheresis donors with a history of one or more pregnancies for both Class I and Class II anti-HLA antibodies using one of two platforms. One is a flow-based assay that yields a quantitative result and the other an enzyme-linked immunosorbent assay (ELISA) that yields either a positive or a negative result (above or below cutoff). STUDY DESIGN AND METHODS: The results of HLA antibody screening tests were analyzed by donor ABO group. Results from large and small American blood collection centers using both platforms were analyzed. Positivity rates were compared by chi-square test and the results stratified by parity using the Mann-Whitney test. RESULTS: No differences in parity were noted among donors of different ABO groups, but a significantly higher rate of HLA antibody positivity was observed among group O donors for the ELISA (31% of group O donors vs. 21% of non-group O donors, p < 0.0001). The higher rate of positivity was primarily due to Class I reactivity. This difference in antibody frequency was not observed at centers using the flow-based assay. CONCLUSION: Centers using the ELISA may have a higher rate of permanent deferral from plateletpheresis donation among group O female donors. Although the reasons for the higher rate of reactivity on Class I ELISA testing are unknown, this could result from test system characteristics or differences in group O donor antibody strength or specificity.

Blood group A and D negativity are associated with symptomatic West Nile virus infection.

BACKGROUND: West Nile virus (WNV) infection is mostly asymptomatic (AS) but 20% of subjects report WNV fever and 1% of patients experience neurologic diseases with higher rates in elderly and immunosuppressed persons. With no treatment and no vaccine to prevent the development of symptomatic (S) infections, it is essential to understand prognostic factors influencing S disease outcome. Host genetic background has been linked to the development of WNV neuroinvasive disease. This study investigates the association between the ABO and D blood group status and WNV disease outcome. STUDY DESIGN AND METHODS: The distribution of blood groups was investigated within a cohort of 374 WNV+ blood donors including 244 AS and 130 S WNV+ blood donors. Logistic regression analyses were used to examine associations between A, B, O, and D blood groups and WNV clinical disease outcome. RESULTS: S WNV+ donors exhibited increased frequencies of blood group A (S 47.6%, AS 36.8%, p = 0.04; odds ratio [OR], 1.56; 95% confidence interval [CI], 1.01-2.40) and D- individuals (S 21.5%, AS 13.1%, p = 0.03; OR, 1.82; 95% CI, 1.04-3.18). CONCLUSION: The findings suggest a genetic susceptibility placing blood group A and D- individuals at risk for the development of S disease outcome after WNV infection.

West Nile virus nucleic acid persistence in whole blood months after clearance in plasma: implication for transfusion and transplantation safety.

BACKGROUND: Previous reports of West Nile virus (WNV) RNA persistence in blood compartments have raised concerns around the remaining risk of WNV transfusion transmission. This study characterized the dynamics of WNV viremia in blood compartments in a longitudinal cohort of 54 WNV-infected blood donors. STUDY DESIGN AND METHODS: Blood samples were collected throughout the year after WNV RNA-positive blood donation (index) and characterized for WNV immunoglobulin (Ig)M and IgG antibodies and for WNV RNA by real-time reverse transcription-polymerase chain reaction. WNV viral loads were compared in plasma and whole blood samples and correlated with blood groups and clinical outcomes. RESULTS: WNV RNA persisted in the red blood cell (RBC) compartment up to 3 months postindex in 42% of the donors. Donors with the highest WNV RNA levels in plasma at index maintained the highest WNV RNA levels in whole blood over the 3 months postindex. Blood group A donors maintained higher postindex WNV viral load in whole blood than blood group O individuals (p = 0.027). Despite a trend for WNV RNA to persist longer in whole blood from symptomatic subjects, no significant association was found between WNV RNA levels in whole blood and disease outcome. CONCLUSION: This study confirmed that WNV RNA persists in the RBC fraction in whole blood and further suggested that the level of persistence in whole blood may be a reflection of initial viral burden in plasma. The association with blood groups suggests that WNV adherence to RBCs may be mediated by molecules overrepresented at the surface of blood group A RBCs.

Tregs control the development of symptomatic West Nile virus infection in humans and mice.

West Nile virus (WNV) causes asymptomatic infection in most humans, but for undefined reasons, approximately 20% of immunocompetent individuals develop West Nile fever, a potentially debilitating febrile illness, and approximately 1% develop neuroinvasive disease syndromes. Notably, since its emergence in 1999, WNV has become the leading cause of epidemic viral encephalitis in North America. We hypothesized that CD4+ Tregs might be differentially regulated in subjects with symptomatic compared with those with asymptomatic WNV infection. Here, we show that in 32 blood donors with acute WNV infection, Tregs expanded significantly in the 3 months after index (RNA+) donations in all subjects. Symptomatic donors exhibited lower Treg frequencies from 2 weeks through 1 year after index donation yet did not show differences in systemic T cell or generalized inflammatory responses. In parallel prospective experimental studies, symptomatic WNV-infected mice also developed lower Treg frequencies compared with asymptomatic mice at 2 weeks after infection. Moreover, Treg-deficient mice developed lethal WNV infection at a higher rate than controls. Together, these results suggest that higher levels of peripheral Tregs after infection protect against severe WNV disease in immunocompetent animals and humans.

Virus and antibody dynamics in acute west nile virus infection.

BACKGROUND: The dynamics of the early stages of West Nile virus (WNV) infection can be assessed by follow-up studies of viremic blood donors. METHODS: A total of 245 donors with WNV viremia were followed up weekly for 4 weeks and then monthly for up to 6 additional months or until seroconversion. Plasma samples were tested for WNV RNA by transcription-mediated amplification (TMA) and for WNV-specific IgM and IgG antibodies. RNA persistence was investigated by 6 replicate TMA tests; samples that were viremic for >40 days were tested for WNV-neutralizing activity. Follow up of 35 additional viremic donors for up to 404 days was conducted to evaluate persistence of WNV-specific antibody. RESULTS: The median time from RNA detection to IgM seroconversion was 3.9 days; to IgG seroconversion, 7.7 days; to RNA negativity by single-replicate TMA, 13.2 days; and to RNA negativity by 6-replicate TMA, 6.1 additional days after results of single-replicate TMA are negative. For 4 donors in whom RNA persisted for >40 days after the index donation, all samples obtained after this threshold were also positive for WNV IgG and neutralizing activity. The mean times to IgM and IgA negativity were 156 and 220 days, respectively. CONCLUSIONS: IgM and IgG develop rapidly after viremia and before RNA levels become undetectable, which occurred a mean of 13.2 days after the index donation among donors in this study. WNV RNA detection by replicate TMA rarely persists for >40 days after the index donation and is accompanied by WNV-specific neutralizing antibody, consistent with an absence of WNV transmission via transfusion of seropositive blood components.

Comprehensive analysis of west nile virus-specific T cell responses in humans.

BACKGROUND: Cellular responses have been shown to play a role in immune control and clearance of West Nile virus (WNV) in murine models. However, little is known about the immunogenic regions of the virus or the phenotype of responding T cells in human infection. METHODS: Frozen peripheral blood mononuclear cells (PBMCs) from 35 WNV-infected blood donors were screened for virus-specific T cell responses by an interferon-gamma (IFN-gamma) enzyme-linked immunosorbent spot assay that used 452 overlapping peptides spanning all WNV proteins. More-detailed phenotypic studies were performed on subjects with high-magnitude T cell responses. RESULTS: In individuals with identified responses, the total number of recognized WNV peptides ranged from 1 to 9 (median, 2 peptides), and the overall magnitude of responses ranged from 50 to 4210 spot-forming cells (SFCs) per 10(6) PBMCs (median, 130 SFCs/10(6) PBMCs). A subset of 8 frequently recognized peptides from the regions of the genome encoding membrane, envelope, and nonstructural 3 and 4b proteins was identified. Phenotypic study of the highest magnitude WNV-specific T cell responses revealed that most were mediated by CD8+ cells that expressed perforin and/or granzyme B. CONCLUSIONS: These findings are the first to define the breadth and characteristics of the human T cell response to WNV and have implications for candidate vaccine design and evaluation.

Safety and donor acceptance of an abbreviated donor history questionnaire.

BACKGROUND: Surveys have shown donor dissatisfaction with the duration of the donation process and repetitive questioning. An abbreviated donor history questionnaire (AQ) may improve satisfaction, but must be safe. STUDY DESIGN AND METHODS: An FDA-approved 34-question AQ was implemented in 2003. Travel, medication, and health history questions were decreased by 18. Donors were eligible for AQ if they had successfully completed three donor suitability assessments on the full-length questionnaire (FQ), including one in the prior 6 months. Data were analyzed from more than 50,000 donations during each of three 20-day periods over the first year of progressive implementation of the AQ. We evaluated the performance of the AQ by comparing donor deferrals for medical history (MHD), physical examination findings (PED), and reactive screening and/or confirmatory tests (RSCT) for viral markers among AQ-ineligible and AQ-eligible donors and separately among AQ-eligible donors who received AQ or FQ. RESULTS: Approximately one-third of presenting donors were AQ-eligible. Use of AQ progressed from 48 percent in October 2003 to 76 percent in November 2004. AQ-eligible donors had lower rates of MHD, PED, and RSCT than donors ineligible for AQ (p < 0.05). Among donors eligible for the AQ, those who received the FQ had slightly more MHD and PED than those who received the AQ (p < 0.05), but there was no difference in RSCT. A postdonation survey indicated significantly increased satisfaction and intent to donate among donors who received the AQ. CONCLUSIONS: In frequent repeat donors, use of an AQ led to increased donor satisfaction and no significant medical concerns about donor or recipient safety.

Two-year experience with aerobic culturing of apheresis and whole blood-derived platelets.

BACKGROUND: Throughout its system of regional centers, Blood Systems implemented culture based bacterial testing with a standardized protocol for both apheresis and whole blood-derived platelets (PLTs). STUDY DESIGN AND METHODS: After a 24-hour hold, 4 mL of PLT product was inoculated into an aerobic bottle (BacT/ALERT, bioMérieux). Cultures were incubated for 24 hours before routine product release to prevent distribution of infected products while minimizing consignee notification, product retrievals, and hospital PLT inventory problems. Initial-positives were further tested (and bacteria identified) by performing cultures from the original component and subcultures from the BacT/ALERT bottle. Results were categorized according to AABB recommended definitions with minor modifications. RESULTS: The rate of true-positive detections from culturing 122,971 apheresis PLTs was 0.017 percent (95% confidence interval [CI], 0.011%-0.026%). All true-positive microorganisms were Gram-positive with a predominance of coagulase-negative Staphylococcus and Bacillus species. Twenty of the 21 true-positive samples (95%) were detected by 24 hours but only 14 (68%) were detected by 18 hours. The false-positive rate due to contamination was 0.1 percent with the majority of isolates being skin or environmental organisms. Results did not differ significantly for whole blood-derived versus apheresis PLTs. CONCLUSION: These data corroborate the fact that the rate of detection of truly contaminated PLT apheresis products in the United States is approximately 1 in 5000 (0.02%); this is lower than the 0.03 to 0.05 percent rates that were generally quoted in the literature before the implementation of prospective bacterial culturing programs.