Characterization of Serum Samples With Discordant Results in 2 Herpes Simplex Virus Type 2 IgG Assays

BACKGROUND

Our laboratory system tests sera for herpes simplex virus type 2 (HSV-2) IgG using the DiaSorin Liaison chemiluminescent immunoassay (CIA), with the option to confirm positive samples by a laboratory-developed HerpeSelect inhibition assay. As part of the confirmation process, the HerpeSelect HSV-2 IgG enzyme immunoassay (EIA) is performed. This study investigated the relationship between DiaSorin HSV-2 IgG CIA-positive indices and HerpeSelect HSV-2 IgG EIA results.

METHODS

HerpeSelect HSV-2 IgG EIA results were compiled for a cohort of consecutive DiaSorin HSV-2 IgG CIA-positive (index ≥1.10) samples. To further characterize DiaSorin CIA-positive samples that were positive (concordant) or negative (discordant) by the HerpeSelect EIA, a separate composite reference study panel was constructed and also tested using the Biokit HSV-2 IgG assay and an HSV-2 IgG inhibition assay developed for the DiaSorin instrument. Samples were classified as DiaSorin HSV-2 IgG true positive or false positive based on a composite reference using HerpeSelect EIA, Biokit, and DiaSorin inhibition results.

RESULTS

Of 2305 consecutive DiaSorin HSV-2 IgG CIA-positive samples, 411 (17.8%) were HerpeSelect HSV-2 IgG EIA negative; 343 of 411 (83%) had DiaSorin indices of 1.10 to 3.00. For the composite reference study panel (N = 120), 59 of 60 discordant samples were classified as DiaSorin HSV-2 IgG false positive based on the composite reference, whereas 58 of 60 concordant samples were classified as true positive.

CONCLUSIONS

Nearly all DiaSorin HSV-2 IgG CIA-positive but HerpeSelect HSV-2 IgG EIA-negative sera are falsely positive in the DiaSorin CIA. Furthermore, most DiaSorin false-positive samples exhibit low-positive indices, suggesting that guidelines for confirmatory testing should include low-positive samples by CIA and EIA.

Duration of West Nile Virus Immunoglobulin M Antibodies up to 81 Months Following West Nile Virus Disease Onset

West Nile virus (WNV) IgM antibodies typically indicate a recent infection. However, WNV IgM antibodies can remain detectable for months to years following illness onset. We found that 23% (11/47) of samples tested with a WNV ELISA and 43% (20/47) of samples tested with WNV microsphere immunoassay (MIA) at 16-19 months following WNV illness onset were positive for IgM antibodies. The proportion of samples testing positive for WNV IgM by ELISA decreased over time, but 5% (2/44) of individuals remained positive at 60-63 months after their acute illness and 4% (2/50) were WNV IgM equivocal at 72-81 months. Testing by MIA showed the same general trend of decreased proportion positive over time though the rates of positivity were higher at most time points compared with the ELISA, including 6% (3/50) of participant's samples identified as IgM positive by MIA at 72-81 months post their acute illness. With the MIA, there also was a high proportion of samples with nonspecific results at each time point; average of 23% across all time points. Clinicians and public health officials should consider these findings along with clinical and epidemiologic data when interpreting WNV IgM antibody test results.

Chikungunya virus infections among travelers-United States, 2010-2013

Chikungunya virus is an emerging threat to the United States because humans are amplifying hosts and competent mosquito vectors are present in many regions of the country. We identified laboratory-confirmed chikungunya virus infections with diagnostic testing performed in the United States from 2010 through 2013. We described the epidemiology of these cases and determined which were reported to ArboNET. From 2010 through 2013, 115 laboratory-confirmed chikungunya virus infections were identified. Among 55 cases with known travel history, 53 (96%) reported travel to Asia and 2 (4%) to Africa. No locally-acquired infections were identified. Six patients had detectable viremia after returning to the United States. Only 21% of identified cases were reported to ArboNET, with a median of 72 days between illness onset and reporting. Given the risk of introduction into the United States, healthcare providers and public health officials should be educated about the recognition, diagnosis, and timely reporting of chikungunya virus disease cases.

Role of cytomegalovirus (CMV) IgG avidity testing in diagnosing primary CMV infection during pregnancy

The risk of intrauterine transmission of cytomegalovirus (CMV) during pregnancy is much greater for women who contract primary CMV infection after conception than for women with evidence of infection (circulating CMV antibodies) before conception. Thus, laboratory tests that aid in the identification of recent primary CMV infection are important tools for managing the care of pregnant women suspected of having been exposed to CMV. CMV IgM detection is a sensitive marker of primary CMV infection, but its specificity is poor because CMV IgM is also produced during viral reactivation and persists following primary infection in some individuals. Studies conducted over the last 20 years convincingly demonstrate that measurement of CMV IgG avidity is both a sensitive and a specific method for identifying pregnant women with recent primary CMV infection and thus at increased risk for vertical CMV transmission. IgG avidity is defined as the strength with which IgG binds to antigenic epitopes expressed by a given protein; it matures gradually during the 6 months following primary infection. Low CMV IgG avidity is an accurate indicator of primary infection within the preceding 3 to 4 months, whereas high avidity excludes primary infection within the preceding 3 months. In this minireview, we summarize published data demonstrating the clinical utility of CMV IgG avidity results for estimating time since primary infection in pregnant women, describe commercially available CMV IgG avidity assays, and discuss some of the issues and controversies surrounding CMV IgG avidity testing during pregnancy.

Reactivity of human IgM binding murine monoclonal 6B6C1 (IgG2a) with other murine monoclonal IgG antibodies

BACKGROUND

Approximately 6% of sera positive in a dengue virus IgM-capture enzyme immunoassay (EIA) represent false-positives due to interaction between IgM and horseradish peroxidase (HRP)-labeled monoclonal antibody (MAb) 6B6C1 (IgG2a). To better understand this interaction, we assessed the reactivity of captured IgM from these sera with other HRP-labeled MAbs.

METHODS

Fifty dengue IgM false-positive sera (recognizing 6B6C1) were evaluated for IgM reactivity with the HRP-labeled MAbs H3A4 (IgG2a), 53.8 (IgG2b), and IL-A2 (IgG1). The sera were also tested in an EIA for human anti-mouse antibody (HAMA).

RESULTS

Forty-three sera (86%) reacted with IgG2a MAb (H3A4). Most (31/43 = 72%) of these sera recognizing 6B6C1 and H3A4 also recognized the IgG2 MAb and/or the IgG1 MAb. In contrast, HAMA was increased in only 9 of 50 (18%) sera reacting with 6B6C1.

CONCLUSIONS

IgM from most sera-binding IgG2a MAb 6B6C1 also binds another IgG2a MAb, suggesting that IgM-6B6C1 reactivity is not idiotype specific. In many cases, IgM recognizing 6B6C1 also binds MAbs of other IgG subclasses, but is negative in a HAMA assay. These findings indicate that samples positive in IgM-capture EIAs utilizing conjugated MAbs should always be retested in the absence of antigen to identify false-positive reactivity caused by direct IgM-MAb interaction.

Neuroinvasive disease and West Nile virus infection, North Dakota, USA, 1999-2008

To determine risk for West Nile virus (WNV) neuroinvasive disease in North Dakota, we tested plasma samples from blood donors for WNV IgG and compared infection rates with reported WNV neuroinvasive disease incidence. We estimate that 1 in 244 WNV infections leads to neuroinvasive disease; risk is substantially increased among men and older persons.

Chikungunya fever in the United States: a fifteen year review of cases

BACKGROUND

Chikungunya virus (CHIKV) represents a threat to the United States, because humans amplify CHIKV and vectors that transmit CHIKV are present.

METHODS

We described the epidemiology of laboratory-confirmed chikungunya fever (CHIK) cases in the United States in 1995-2009 and compared states with CHIKV vectors with states with returning viremic CHIK cases. For 2006-2009, we evaluated reporting of CHIK cases to ArboNET, the arboviral surveillance system.

RESULTS

In 1995-2009, 109 CHIK cases were identified in the United States; all adult travelers. Sixty-two subjects (57%) had recently visited India, and 13 (12%) had CHIKV viremia. Of the 26 jurisdictions with CHIK cases, 22 (85%) reported the presence of CHIKV vectors. Twelve viremic travelers returned to 6 states with CHIKV vectors. Of the 106 cases identified in 2006-2009, only 27 (25%) were reported to ArboNET, with a median of 122 days (range, 44-273 days) between illness onset and reporting.

CONCLUSIONS

No locally acquired CHIK cases were identified. However, several viremic travelers returned to states with CHIKV vectors and presented a risk for local transmission. Incomplete and delayed reporting made ArboNET less useful. To minimize the risk of CHIKV spread in the United States, healthcare providers and public health officials should be educated about recognition, diagnosis, and reporting of CHIK cases.

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.

Culture-Associated Enhancement of Lecam-1 Expression by Lymphocytes and Partial Inhibition of Enhancement by IL-4

Recent studies have shown that the human leukocyte endothelial cell adhesion molecule-1 (LECAM-1) functions as a homing receptor, mediating leukocyte binding to high endothelial venules in peripheral lymph nodes. Increasing evidence has demonstrated that cytokines, such as IL-4, can modulate the expression of surface proteins such as homing receptors on a variety of cells. We thus investigated the modulatory effects of cytokines on LECAM-1 expression by lymphocytes using single- and dual-color flow cytometry. We found that the density of LECAM-1 expression increased markedly during 3 days of culture and that this culture-associated enhancement (CAE) of LECAM-1 expression was significantly inhibited by IL-4. B cells and both major T cell subsets (CD4, CD8) exhibited CAE of LECAM-1 expression, but the inhibitory effect of IL-4 on this response occurred only in the T cell populations. The inhibitory effect of IL-4 on enhanced LECAM-1 expression was reversible, and characterized all 3 LECAM-1 epitopes assessed. Natural killer cells, in contrast, did not exhibit CAE of LECAM-1 expression, and IL-4 had no modulatory effect on LECAM-1 expression by these cells. Another adhesion molecule, CD44, showed enhanced expression during culture, but this enhancement was not inhibited by IL-4. The results show that LECAM-1 expression by T and B lymphocytes is significantly increased during culture and that the inhibitory effect of IL-4 on this increase is restricted to T cells. These findings suggest that IL-4, generated during an immune response, may play a role in regulating the migration and localization of T lymphocytes to lymphoid tissues.

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.

Interferon and interferon-induced chemokine expression is associated with control of acute viremia in West Nile virus-infected blood donors

To understand early host responses controlling West Nile virus (WNV) infection, acutely viremic blood donors, identified by nucleic acid amplification testing, were enrolled and monitored for RNA-clearance and WNV-specific IgM and IgG antibodies. Viral load and chemokine and cytokine assays were performed on serial samples from donors whose index and first follow-up samples tested negative for IgM. A total of 84% of the specimens obtained from viremic donors before IgM/IgG seroconversion demonstrated a decreasing viral load. Levels of interferon (IFN)-α ere significantly increased before IgM seroconversion, relative to those in control specimens. CXCL10 and CCL2 were significantly elevated in donor specimens obtained before IgM seroconversion, compared with those obtained after IgM seroconversion. These findings suggest that IFN-mediated innate immunity plays a key role in initial control of WNV replication.

Evaluation of enzyme-linked immunosorbent assays for detecting circulating antibodies to Candida albicans

Published studies indicate that Candida albicans antibody assays utilizing cytoplasmic antigens offer greater utility for identifying cases of systemic candidiasis when compared with assays utilizing cell wall components. We assessed the performance characteristics of a commercially available system that utilizes cytoplasmic antigens to measure C. albicans IgG, IgM, and IgA (Candida Detect ELISA reagents). Intra-assay variation was < or =5%, inter-assay variation was < or =10%, and good linearity was observed for all the three antibody isotypes. Results for specimens stored under various conditions were comparable to those obtained initially. Inter-laboratory reproducibility was excellent; qualitative concordance was > or =93% for all the three isotypes, with slopes and R(2) values approaching 1.0 in linear regression analyses. Seroprevalence in persons without apparent systemic candidiasis was evaluated using three different serum panels; seroprevalence rates ranged from 24 to 32% for IgG, 2-14% for IgM, and 15-36% for IgA. Seroprevalence rates in a panel of sera containing antibodies to other fungi were similar to rates observed in panels from individuals without systemic candidiasis. These findings demonstrate the acceptable performance of assay systems employing Candida Detect ELISA reagents.

Identification of interferon-beta antibodies in a reference laboratory setting: Findings for 1144 consecutive sera

Clinical studies demonstrate differences in interferon-beta (IFNbeta) antibody detection frequencies among multiple sclerosis patients receiving different IFNbeta products. We sought to determine if these differences are also found when IFNbeta antibodies are measured in a reference laboratory, where factors normally controlled in clinical studies are unknown. Serum IFNbeta binding antibodies (BAbs) were quantitated by ELISA; BAbs-positive samples were then tested in a bioassay for neutralizing antibodies (NAbs). Consistent with clinical studies, frequencies of BAbs-positive sera and NAbs-positive sera were lower in the Avonex (IFNbeta-1a) treatment group than Rebif (IFNbeta-1a) and Betaseron (IFNbeta-1b) groups. We further identified a predictive relationship between positive BAbs levels and NAbs activity in patients treated with IFNbeta-1a products, but not those treated with IFNbeta-1b.

Persistence of West Nile virus-specific antibodies in viremic blood donors

We evaluated West Nile virus (WNV) antibody persistence by using follow-up plasma samples from 35 blood donors who made viremic donations in 2005. At 26 to 34 days of follow-up, all of the donors (n = 33) were positive for WNV immunoglobulin M (IgM), IgA, and IgG. At 1-year of follow-up, 17% of the donors (n = 23) were positive for WNV IgM, 57% were positive for WNV IgA, and 100% were positive for WNV IgG.

Further comparisons of assays for detecting MAG IgM autoantibodies

Anti-MAG antibodies are commonly found in the sera of patients with demyelinating sensorimotor neuropathy and IgM paraproteinemia. Our objective here was to compare MAG results obtained by two different laboratories using similar methods (Western blot, EIA, IFA). Western blot (WB) employing MAG from monkey was less sensitive (72.5%) than myelin IFA (92.5%; monkey nerve) and EIA (97.5%; human MAG) when compared to WB using human MAG and is most likely due to methodology (not antigen source). EIA detected low titers of MAG IgM antibodies in suspected patient sera (negative by other methods) that were also SGPG IgM-positive. Patients having low titers by EIA, but negative by WB may have other autoimmune neuropathies without demyelination.

Utilization of hantavirus antibody results generated over a five-year period to develop an improved serologic algorithm for detecting acute Sin Nombre hantavirus infection

In the United States most cases of hantavirus pulmonary syndrome (HPS) are caused by the Sin Nombre virus (SNV) and are typically identified by serology. The goal of this study was to assess the performance of our hantavirus serologic testing algorithm by reviewing results generated over five years. Sera were screened for pan-hantavirus immunoglobulin (Ig)G and IgM by enzyme-linked immunosorbent assay (ELISA). Screen IgG+ sera were then tested by immunoblot for SNV glycoprotein-specific IgG, and screen IgM+ sera were tested for SNV-specific IgM using an ELISA that measured differential reactivity to SNV and Seoul nucleocapsid proteins. Although only 13% of sera were positive in one or both screening assays, 85% of screen+sera lacked SNV antibodies. Nearly all (97%) screen IgM-IgG+ samples lacked SNV IgG, and 90% of screen IgM+IgG- samples lacked SNV IgM. However, SNV IgM testing of screen IgM+IgG- samples appears to be necessary, since this test identified nine of 37 patients with acute HPS (based on clinical feedback). A screen IgM+IgG+ result was a good predictor of SNV antibody detection and acute HPS. These findings were used to design a modified algorithm that identified all 37 patients with acute HPS, but reduced the number of specimens that required SNV antibody testing by 42%.

West Nile virus immunoglobulin A (WNV IgA) detection in cerebrospinal fluid in relation to WNV IgG and IgM reactivity

BACKGROUND

Diagnostic criteria for neurologic involvement in WNV infection include WNV IgM detection in CSF; however, WNV IgM can persist in CSF >6 months. CSF IgA characterizes other flavivirus infections, but WNV IgA in CSF has not been evaluated. WNV IgM in CSF correlates with IgM in serum but the presence of WNV IgA in CSF compared to serum is unknown.

OBJECTIVES

Evaluate WNV IgA detection in CSF as a marker of WNV neuroinvasive infection, initially with samples pre-selected based on WNV IgG and IgM reactivity and subsequently with all available CSF samples submitted for WNV antibody testing over an entire WNV season.

STUDY DESIGN

Selected CSF samples and CSF/serum pairs previously tested for WNV IgG and IgM were assayed for WNV IgA. Subsequently, all available CSF samples tested for WNV antibodies during the 2005 season were tested for WNV IgA, including those where paired sera were available and tested for IgA, IgG and IgM.

RESULTS

For most samples, including paired CSF and serum, the IgA result qualitatively agreed with the IgM result, regardless of the IgG result.

CONCLUSION

IgA detection is equivalent to IgM detection as a marker of WNV infection in CSF.

West Nile virus infections projected from blood donor screening data, United States, 2003

Routine donor nucleic acid amplification testing is a valuable surveillance screening tool.

National blood donor screening for West Nile virus (WNV) RNA using minipool nucleic acid amplification testing (MP-NAT) was implemented in the United States in July 2003. We compiled national NAT yield data and performed WNV immunoglobulin M (IgM) testing in 1 WNV-epidemic region (North Dakota). State-specific MP-NAT yield, antibody seroprevalence, and the average time RNA is detectable by MP-NAT were used to estimate incident infections in 2003. WNV donor screening yielded 944 confirmed viremic donors. MP-NAT yield peaked in August with >0.5% of donations positive for WNV RNA in 4 states. Peak IgM seroprevalence for North Dakota was 5.2% in late September. The average time viremia is detectable by MP-NAT was 6.9 days (95% confidence interval [CI] 3.0–10.7). An estimated 735,000 (95% CI 322,000–1,147,000) infections occurred in 2003, with 256 (95% CI 112–401) infections per neuroinvasive case. In addition to preventing transfusion-transmitted WNV infection, donor screening can serve as a tool to monitor seasonal incidence in the general population.

Evaluation of the INOVA diagnostics enzyme-linked immunosorbent assay kits for measuring serum immunoglobulin G (IgG) and IgA to deamidated gliadin peptides

New assays for antibodies to deamidated gliadin peptides (DGP) expressing celiac disease-specific epitopes were evaluated using 154 sera previously tested for endomysial immunoglobulin A (IgA) (EMA), transglutaminase IgA (TGA), and conventional gliadin antibodies. DGP antibody results showed 97% concordance with EMA and TGA results. Of 56 sera negative for EMA and TGA but positive for conventional gliadin antibodies, 54 (96%) were negative for DGP antibodies.

Biomarkers for diagnosing and monitoring autoimmune diseases

The goal of studies of autoimmune disease biomarkers is to identity markers that fluctuate with disease development and severity, but then normalize following successful therapy. The perfect marker could thus serve as a diagnostic tool, as well as a monitoring device for therapeutic drug efficacy. Current biomarker discovery efforts are focused on three groups of proteins reflective of the autoimmune disease process: (1) degradation products arising from destruction of affected tissues, (2) enzymes that play a role in tissue degradation and (3) cytokines and other proteins associated with immune activation. Potential biomarkers for two autoimmune diseases, rheumatoid arthritis and multiple sclerosis, have been described in recent publications. For rheumatoid arthritis, these markers (by group) include (1) aggrecan fragments, C-propeptide of type II collagen and cartilage oligomeric matrix protein, (2) matrix metalloprotease (MMP)-1, MMP-3 and MMP-1/inhibitor complexes and (3) thioredoxin, IL-16 and tumour necrosis factor (TNF)-alpha. For multiple sclerosis, they include (1) neurofilament light protein and glial fibrillary acidic protein, (2) MMP-2 and MMP-9 and (3) TNF-alpha and soluble vascular adhesion molecule-1. The utility of most of these markers is limited by their restriction to relatively inaccessible anatomic sites (synovial or cerebrospinal fluid). Thus, from a practical standpoint, the most useful autoimmune biomarkers will be those measurable in serum or plasma.

Evaluation of a tetraplex microsphere assay for Bordetella pertussis antibodies

To increase testing efficiency, a microsphere-based multianalyte immune detection (MAID) system was developed to measure serum immunoglobulin G (IgG) and IgA recognizing two Bordetella pertussis antigens, pertussis toxin (PT) and filamentous hemagglutinin antigen (FHA). The assay was performed as two separate duplexes. One duplex measured IgG to PT and FHA, and the other measured IgA to PT and FHA. The two duplexes were then combined and analyzed as a tetraplex. The MAID system and an in-house enzyme-linked immunosorbent assay (ELISA) system were used to evaluate 100 sera from blood donors and 220 consecutive sera submitted for B. pertussis antibody testing. For both the MAID and ELISA systems, antibody levels were defined as increased if greater than the blood donor group 95th percentile value. The qualitative concordance rates between MAID and ELISA results for the 220 consecutively submitted sera were as follows: PT IgG, 99%; PT IgA, 94%; FHA IgG, 93%; FHA IgA, 94%. The overall concordance rate was 95% (836 of 880 result sets). For 29 of 44 (66%) discordant result sets, the discordant MAID result was supported by the MAID and ELISA results for other B. pertussis antibodies. The MAID and in-house ELISA systems were also used to evaluate 20 sera previously tested for pertussis antibodies at a pertussis vaccine research laboratory; MAID results for all four analytes did not significantly differ from results obtained by the research laboratory. These findings show that antibodies to B. pertussis antigens can be measured easily and accurately using a tetraplex microsphere system.

West Nile Virus Infections Projected from Blood Donor Screening Data, United States, 2003

National blood donor screening for West Nile virus (WNV) RNA using minipool nucleic acid amplification testing (MP-NAT) was implemented in the United States in July 2003. We compiled national NAT yield data and performed WNV immunoglobulin M (IgM) testing in 1 WNV-epidemic region (North Dakota). State-specific MP-NAT yield, antibody seroprevalence, and the average time RNA is detectable by MP-NAT were used to estimate incident infections in 2003. WNV donor screening yielded 944 confirmed viremic donors. MP-NAT yield peaked in August with >0.5% of donations positive for WNV RNA in 4 states. Peak IgM seroprevalence for North Dakota was 5.2% in late September. The average time viremia is detectable by MP-NAT was 6.9 days (95% confidence interval [CI] 3.0-10.7). An estimated 735,000 (95% CI 322,000-1,147,000) infections occurred in 2003, with 256 (95% CI 112-401) infections per neuroinvasive case. In addition to preventing transfusion-transmitted WNV infection, donor screening can serve as a tool to monitor seasonal incidence in the general population.

Development and persistence of West Nile virus-specific immunoglobulin M (IgM), IgA, and IgG in viremic blood donors

West Nile Virus (WNV) antibody development and persistence were investigated in blood donors who made WNV RNA-positive (viremic) donations in 2003. Plasma samples from the index donations and follow-up serum or plasma samples were tested for WNV immunoglobulin M (IgM), IgA, and IgG by using enzyme-linked immunosorbent assays. Antibody development was investigated with 154 samples collected from 84 donors 1 to 21 days after their RNA-positive, antibody-negative, index donation. WNV IgM and IgA were first detected on day 3, and all samples collected after day 9 were WNV IgM and IgA positive; WNV IgG was first detected on day 4, and all samples collected after day 16 were positive. Antibody persistence in this donor group (index donations antibody negative) was evaluated by using 128 samples collected from 89 donors on days 22 to 440 of follow-up; 88% of samples were WNV IgM positive, 86% were WNV IgA positive, and 100% were WNV IgG positive. In linear regression analysis, trendlines for WNV IgM and IgA reached the value discriminating positive from negative results at 218 days and 232 days of follow-up, respectively. Similar WNV IgM and IgA persistence trends characterized 27 donors whose index samples were positive for WNV IgM and IgA, as well as 14 donors whose index samples were positive for WNV IgG but negative for WNV IgM. These findings show that WNV IgG emerges after WNV IgM and IgA and that both WNV IgM and IgA typically persist for at least 6 months after infection. Thus, unlike some other flavivirus infections, WNV infection is not characterized by a relatively rapid disappearance of virus-specific IgA.

Utilization of follow-up specimens from viremic blood donors to assess the value of west nile virus immunoglobulin G avidity as an indicator of recent infection

The value of West Nile virus immunoglobulin G avidity for distinguishing recent from past infection was investigated using 348 follow-up specimens from 170 viremic blood donors. Low avidity accurately indicated infection within the previous 4 months. However, due to rapid avidity maturation in some individuals, high avidity did not accurately indicate past infection.

Evaluation of a West Nile virus immunoglobulin A capture enzyme-linked immunosorbent assay

An in-house-developed enzyme-linked immunosorbent assay detected West Nile virus (WNV) immunoglobulin A (IgA) in 65 of 68 sera from WNV-infected patients; 40 of 63 WNV IgM-positive, IgG-negative serum or plasma specimens; 65 of 67 WNV IgM-positive, IgG-positive specimens; 0 of 70 WNV IgM-negative, IgG-negative specimens; and 0 of 64 archived blood donation sera. WNV IgA is thus highly prevalent among WNV-infected patients and typically appears after WNV IgM but before WNV IgG.

Detection of West Nile virus RNA and antibody in frozen plasma components from a voluntary market withdrawal during the 2002 peak epidemic

BACKGROUND

The US West Nile virus (WNV) epidemic in the summer and fall of 2002 included the first documented cases of transfusion-transmitted WNV infection. In December 2002, the FDA supported a voluntary market withdrawal by the blood banking community of frozen blood components collected in WNV high-activity areas. At the time, the prevalence of viremia and serologic markers for WNV in the blood supply was undefined.

STUDY DESIGN AND METHODS

In collaboration with America's Blood Centers, 1468 frozen plasma components (of approx. 60,000 frozen units voluntarily withdrawn from the market) were selectively retrieved from the peak epidemic regions and season (June 23, 2002-September 28, 2002). These units were unlinked, subaliquoted, and tested by WNV enzyme immunoassays (EIAs; Focus Technologies and Abbott Laboratories) and nucleic acid amplification tests (NATs; Gen-Probe Inc. and Roche Molecular Systems).

RESULTS

Of the 1468 EIA results from Abbott and Focus, 7 were anti-immunoglobulin M (IgM)- and anti-immunoglobulin G (IgG)-reactive by both assays, 8 and 1 were IgM-only-reactive, and 8 and 23 were IgG-only-reactive, respectively. NAT by Gen-Probe and Roche Molecular Systems yielded one RNA-positive, antibody-negative unit containing approximately 440 RNA copies per mL. An additional 10-fold replicate NAT testing by Gen-Probe on 14 of 15 IgM-reactive specimens yielded 2 additional IgM- and IgG-reactive units with low-level viremia (i.e., 7/10 and 2/10 replicates tested reactive).

CONCLUSION

The prevalence of acute (RNA-positive) and recent (IgM-seroreactive) WNV infections indicates that transfusion risk in high-risk areas could have been considerable and that voluntary market withdrawal of frozen components likely averted some WNV transfusion transmissions. The existence of very-low-level viremic units raises concerns, because WNV minipool NAT screening will miss such units and individual NAT may not completely correct this situation.

Performance of immunoglobulin G (IgG) and IgM enzyme-linked immunosorbent assays using a West Nile virus recombinant antigen (preM/E) for detection of West Nile virus- and other flavivirus-specific antibodies

Focus Technologies developed an indirect immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) and a mu-capture IgM ELISA for the detection of West Nile virus (WNV)-specific antibodies based on a WNV preM/E protein recombinant antigen. Normal and disease state serum panels were used to assess the performance characteristics of the two WNV ELISA kits. Totals of 807 and 1,423 sera were used to assess the IgG ELISA and IgM ELISA kits, respectively. The Focus Technologies IgG ELISA had a sensitivity of 97.6% and a specificity of 92.1% (excluding non-WNV flavivirus sera). The comparative method for WNV IgG may lack sensitivity in detecting IgG in early WNV infection, so the specificity of the Focus IgG ELISA may be higher than 92.1%. When sera from patients either infected with or vaccinated against other flaviviruses were tested on the WNV IgG assay, 35% of the sera reacted as positive for WNV IgG. Yellow fever and Japanese encephalitis vaccinees were less reactive in the IgG ELISA than St. Louis and dengue fever patients. The Focus Technologies IgM ELISA had a sensitivity and a specificity of 99.3% (excluding the non-WNV flavivirus sera). The overall cross-reactivity for the IgM ELISA to flavivirus sera was 12%, with 31% of St. Louis encephalitis patients found to be WNV IgM positive and no yellow fever vaccinees found to be WNV IgM positive. In a selected population of 706 sera, 15 false-positive WNV IgM sera were identified. The use of a background subtraction method for the IgM ELISA eliminated all 15 false-positive results, giving a specificity of 100% for the Focus IgM ELISA.

Utility of the focus technologies west nile virus immunoglobulin M capture enzyme-linked immunosorbent assay for testing cerebrospinal fluid

Focus Technologies has developed an immunoglobulin M (IgM) capture enzyme-linked immunosorbent assay (ELISA) kit that utilizes recombinant West Nile virus (WNV) antigens to detect WNV IgM in serum. We evaluate here the utility of the kit for detecting WNV IgM in cerebrospinal fluid (CSF). The sensitivity was evaluated by using 52 CSF specimens from the 2002 WNV season that were positive in both the Public Health Service Laboratories WNV IgM ELISA and an in-house WNV IgM ELISA with native WNV antigen. The specificity was evaluated with two groups of specimens: (i). 73 CSF specimens submitted for in-house WNV IgM ELISA testing from February through April 2003 and yielding a negative WNV IgM result and (ii). 60 CSF specimens determined to be positive for another virus by PCR testing. Using these 185 CSF specimens at a screening dilution of 1:2, the kit was determined to be 100% sensitive and 100% specific. Endpoint titers were determined for 20 IgM-positive CSF specimens by testing serial twofold dilutions and ranged from 1:8 to 1:512. Index values (specimen absorbance value/calibrator absorbance value) for the screening dilution (1:2) showed no correlation with IgM titers, whereas index values for higher dilutions showed significant correlation with IgM titers. CSF screening dilutions of greater than 1:2 are not recommended, however, due to the risk of obtaining false-negative results. These findings show that the Focus Technologies WNV IgM capture ELISA, when utilized as recommended, offers accurate qualitative detection of WNV IgM in CSF specimens.

Detection of West Nile virus (WNV)-specific immunoglobulin M in a reference laboratory setting during the 2002 WNV season in the United States

Between 1 June and 31 December 2002, 30,677 serum samples and 4,554 cerebrospinal fluid (CSF) samples were tested for West Nile virus (WNV)-specific immunoglobulin M (IgM) by an in-house enzyme-linked immunosorbent assay (ELISA); 1,481 serum samples (4.8%) and 345 CSF samples (7.6%) were positive for WNV IgM. Positive samples were forwarded to public health service laboratories (PHSLs) for further testing. PHSLs supplied results from their WNV IgM ELISAs for 654 samples; 633 (97%) were positive. PHSLs supplied WNV plaque reduction neutralization test results for 128 samples; 123 (96%) were positive. WNV IgM seroconversion and seroreversion trends were evaluated for 749 patients who each provided two serum samples that were tested during the study period. Of 574 patients whose first serum sample was IgM negative, 41 (7%) seroconverted (the second serum sample was IgM positive); of 175 patients whose first serum sample was IgM positive, 22 (13%) seroreverted (the second serum sample was IgM negative). The seroreversion rate was directly proportional to the time between serum sample collection; whereas only 1% of patients whose sera were collected <20 days apart showed seroreversion, 54% of patients whose sera were collected >60 days apart showed seroreversion. Conversion and reversion trends for CSF were evaluated for 68 patients. Of 54 patients whose first CSF specimen was IgM negative, 9 (17%) converted; none of 14 patients whose first CSF specimen was IgM positive reverted. Concomitant detection of WNV IgM in serum and CSF was assessed for 1,188 patients for whom paired serum and CSF specimens were available; for all 130 patients for whom IgM was detectable in CSF, IgM was also detectable in serum. These findings show that an in-house WNV IgM ELISA accurately identifies patients with WNV infection, document WNV IgM conversion and reversion trends, and demonstrate that WNV IgM detection in CSF is accompanied by WNV IgM detection in serum.

Comparison of complement fixation and hemagglutination inhibition assays for detecting antibody responses following influenza virus vaccination

Complement fixation (CF) was compared to hemagglutination inhibition (HI) as a method for identifying antibody responses to influenza virus vaccination. CF assays were performed at two different laboratories using paired (pre- and postvaccination) sera from 38 vaccinated laboratory employees; HI assays were performed at a third laboratory. As expected, most vaccinees (31/38 = 82%) responded to at least one of three influenza virus antigens as measured by HI. In contrast, only 21% (8/38) of vaccinees showed a response by CF at laboratory 1, and only 29% (11/38) showed a response by CF at laboratory 2. These findings indicate that due to low sensitivity, CF assays should not be used to assess the antibody response to influenza virus vaccination.

Performance characteristics of an in-house assay system used to detect West Nile Virus (WNV)-specific immunoglobulin M during the 2001 WNV season in the United States

During the 2001 U. S. West Nile virus (WNV) season, 163 specimens were reactive in an in-house WNV-specific immunoglobulin M (IgM) screening enzyme-linked immunosorbent assay (ELISA) and were referred to either the Centers for Disease Control and Prevention or the appropriate state public health laboratory (CDC/SPHL) for additional testing. CDC/SPHL supplied results for 124 specimens that could be further evaluated in-house: 70 specimens were nonreactive in the CDC/SPHL WNV-specific IgM screening assay, and 54 specimens were reactive. These specimens were used to evaluate a modified in-house WNV-specific IgM ELISA that incorporated background subtraction to identify nonspecific reactivity and thus improve assay specificity. Of the 70 CDC/SPHL nonreactive samples, 49 (70%) were nonreactive in the modified ELISA; of the 54 CDC/SPHL reactive samples, 51 (94%) were reactive in the modified ELISA. Confirmatory studies performed by CDC/SPHL indicated that 38 CDC/SPHL screen-reactive specimens represented true WNV infection; all 38 specimens were reactive in the modified in-house WNV-specific IgM ELISA. These findings demonstrate that an in-house ELISA system for WNV-specific IgM effectively identifies patients with WNV infection.

Validation of an in-house assay for cytomegalovirus immunoglobulin G (CMV IgG) avidity and relationship of avidity to CMV IgM levels

Measurement of cytomegalovirus (CMV)-specific immunoglobulin G (IgG) avidity has proven to be a powerful tool for distinguishing primary from nonprimary CMV infection. An in-house enzyme-linked immunosorbent assay (ELISA) for measuring CMV IgG avidity was validated using 84 sera from pregnant women who had recently seroconverted following primary CMV infection and 74 sera from individuals with past CMV infection (IgG-positive and IgM-negative profile). Of the 84 sera from pregnant women, 73 sera were collected within 120 days of the last IgG-negative sample, and 72 of these 73 sera (99%) exhibited an avidity index (AI) of <50%. In contrast, 71 of 74 (96%) sera from individuals with past CMV infection exhibited CMV AI values of > 60%. Thus, low avidity in the in-house ELISA was defined as an AI of < or = 50%, whereas high avidity was defined as an AI of > or = 60%. In additional studies, the relationship between CMV IgG avidity and CMV IgM levels was examined using 64 CMV IgG-positive sera (time since seroconversion unknown) exhibiting equivocal or positive results in a CMV IgM capture ELISA (Diamedix). Of these 64 sera, 29 exhibited IgM index values of > or = 3.0, and 27 of these 29 (93%) exhibited low IgG avidity. A similar trend was observed when a subset of these 64 sera (n = 48) was tested in another CMV IgM capture ELISA (Trinity); of 18 sera with IgM index values of > or = 3.0, 17 (94%) exhibited low IgG avidity. These findings demonstrate the validity of an in-house ELISA for CMV IgG avidity and further show that strong reactivity of CMV IgG-positive sera in either of two CMV IgM capture assays is a reliable indicator of low CMV IgG avidity, and thus, recent CMV infection.

Performance characteristics of the PolyTiter Immunofluorescent Titration system for determination of antinuclear antibody endpoint dilution

Conventional screening for circulating antinuclear antibodies (ANA) is generally performed by immunofluorescent (IF) microscopy with a 1:40 dilution of serum. Intensity of IF staining is then semiquantitated by using twofold serial dilutions, where the highest dilution in which staining intensity equals the endpoint control is expressed as an endpoint titer. The PolyTiter Immunofluorescent Titration system (Polymedco, Inc.) facilitates ANA-IF assay (IFA) testing by relating the intensity of IF staining to reference calibrators (defined in PolyTiter units), providing an endpoint titer directly from a 1:40 dilution. This study was conducted to assess the performance characteristics of the PolyTiter system. Two technologists each evaluated 10 replicates of three specimens and two controls on five sequential days. Endpoint dilution agreement (defined as +/-2 dilutions) with the reference was 100% for all controls and for all specimens by one technologist. The second reader reported agreement of 98, 88, and 100% for the low, medium, and high specimens, respectively. Analysis of PolyTiter unit values yielded between-reader, between-run, and within-run precision coefficients of variation of less than 10%. The variance component in the lot-to-lot analysis was zero, indicating all of the variation was due to run-to-run differences. Overall endpoint dilution agreement between PolyTiter and serial dilution in the evaluation of 125 specimens at three sites was 90, 93, and 86%. Pattern identification with the PolyTiter was similar to that with serial dilution. The PolyTiter system demonstrates acceptable performance for routine ANA-IFA testing in the clinical laboratory.

Simplified assay for measuring Toxoplasma gondii immunoglobulin G avidity

A Toxoplasma gondii immunoglobulin G (IgG) avidity enzyme-linked immunosorbent assay (ELISA) was developed that combines the accuracy of assays based on end point titers and the relative ease of assays based on optical density values. Like published procedures, the new assay's avidity index (AI) was based on differential T. gondii-specific IgG reactivity in serum-treated wells washed with urea buffer versus that in wells washed with control buffer; unlike previous assays, however, the IgG reactivity was measured quantitatively using a standard curve. The assay was evaluated using 24 IgG-positive and IgM-positive sera collected within 5 months of the onset of symptoms (recent-infection group) and 25 IgG-positive and IgM-negative sera (past-infection group). All sera in the recent-infection group exhibited AI values of <0.18, whereas all sera in the past-infection group exhibited AI values of >0.27. The AI values of the recent-infection group showed significant correlation with the number of days after the onset of symptoms. A subset of 16 sera (8 recent and 8 past) was tested using a commercially available T. gondii IgG avidity ELISA based on end point titration; the results of the two assays showed highly significant correlation (R(2) = 0.9125). In addition, we confirmed and extended the findings of other investigators, showing that AI values calculated using optical density values, but not AI values calculated using quantitative IgG values, varied significantly depending on the serum dilution used. This new assay should facilitate the accurate measurement of T. gondii IgG avidity in a reference laboratory setting.

Immunoglobulin A (IgA) deficiency and alternative celiac disease-associated antibodies in sera submitted to a reference laboratory for endomysial IgA testing

Immunoglobulin A (IgA) deficiency occurs more frequently in patients with celiac disease (CD) than in the general population and can lead to false-negative results in the best serologic test for CD, endomysial IgA (EMA). To evaluate the impact of IgA deficiency on serologic detection of CD in a reference laboratory setting, IgA levels were measured in 510 consecutive serum specimens submitted for testing for EMA; 510 consecutive serum specimens submitted for Helicobacter pylori IgG testing served as a gastrointestinal symptom control group. The frequency of IgA deficiency was significantly higher among the specimens submitted for testing for EMA (5.1%) than among the specimens from the symptom control group (1.4%). Three subsets of sera from the group of specimens submitted for testing for EMA were then tested by additional serologic assays for CD; these subsets were EMA-positive sera (n = 25), EMA-negative, IgA-deficient sera (n = 26), and control sera (from EMA-negative, IgA-nondeficient patients age matched to IgA-deficient patients; n = 26). The proportions of EMA-positive sera positive by other assays for CD were 92% for transglutaminase IgA (TG-IgA), 80% for gliadin IgA, 84% for gliadin IgG, 60% for endomysial IgG (EMG), and 32% for transglutaminase IgG (TG-IgG). Very low proportions (0 to 8%) of IgA-deficient sera and control sera were positive for TG-IgA, gliadin IgA, EMG, and TG-IgG. Eight of 26 (31%) IgA-deficient serum samples were positive for gliadin IgG, whereas 3 of 26 (12%) control serum samples were positive for gliadin IgG, but this difference was not statistically significant. Physicians supplied clinical data for 18 of 26 patients with IgA deficiency; only 4 patients had undergone small-bowel biopsy, and 0 of 4 patients showed villous atrophy. These findings show that IgA deficiency is found more frequently among sera submitted for testing for EMA in a reference laboratory setting, but there was no clear-cut serologic or clinical evidence of CD in EMA-negative, IgA-deficient patients.

Evaluation of an enzyme immunoassay system for measuring herpes simplex virus (HSV) type 1-specific and HSV type 2-specific IgG antibodies

MRL Diagnostics has developed a dual enzyme immunoassay (EIA) system that employs the recombinant Herpes Simplex Virus (HSV) type-specific glycoproteins G1 (HSV1) and G2 (HSV2) to detect HSV type-specific IgG antibodies. This system was evaluated using 155 consecutive sera previously tested in a conventional dual EIA system (Zeus) that employs multiple HSV1 and HSV2 proteins to detect type-common as well as type-specific antibodies. Sera were also analyzed by Western blot to determine the true HSV type-specific IgG reactivity pattern. Of 110 sera giving concordant reactivity patterns in the MRL and Zeus EIA systems, 108 (98%) also displayed concordant Western blot patterns; two sera gave false positive HSV2 reactivity in both EIA systems. Of 45 sera giving discordant MRL and Zeus EIA reactivity patterns, 41 (91%) displayed a Western blot reactivity pattern that matched the MRL reactivity pattern. Both the HSV1 IgG component and the HSV2 IgG component of the MRL EIA system were 100% sensitive and > 95% specific. In contrast, the Zeus HSV1 IgG EIA was 98% sensitive and 79% specific, and the Zeus HSV2 IgG EIA was 85% sensitive and 79% specific. An analysis of the distribution of index values in the MRL EIA system showed that low-positive values (1.0-3.0) were rare, but, when detected, often represented false positive results; only 11 MRL low-positive results were observed, but all 6 MRL false positive results were found within this low-positive subgroup. These findings show that the MRL dual EIA system effectively detects HSV type-specific IgG antibodies.

Evaluation of a line immunoblot assay for detection of antibodies recognizing extractable nuclear antigens

Sera (n = 90) giving positive results in a screening test for antibodies to extractable nuclear antigens (ENAs) were tested in a line immunoblot assay that measures antibody reactivity with individual ENAs in a single test field. Results were then compared to those obtained in monospecific ENA antibody enzyme immunoassays (EIAs). Discordant results were resolved by immunodiffusion. Of 540 result pairs (90 sera tested for 6 ENAs [Sm/RNP, Sm, SSA, SSB, Scl-70, Jo-1]), 509 (94%) showed concordance. Immunodiffusion resolved 28 of 31 discordant result pairs in favor of the immunoblot result. After resolution of discordant data, the immunoblot assay exhibited 100% sensitivity for all ENA antibodies except those recognizing Scl-70, for which the sensitivity was 89%; specificity was over 96% for all 6 ENA antibodies. These findings show that a line immunoblot assay for the characterization of ENA antibodies yields results comparable to those obtained using monospecific ENA antibody EIAs. The immunoblot assay is easier and less expensive to perform due to its utilization of a single test field.

Elevated CD38 antigen expression on CD8+ T cells is a stronger marker for the risk of chronic HIV disease progression to AIDS and death in the Multicenter AIDS Cohort Study than CD4+ cell count, soluble immune activation markers, or combinations of HLA-DR and CD38 expression

The prognostic value of several immunologic markers were compared in Los Angeles Multicenter AIDS Cohort Study (MACS) participants, most of whom had been infected with HIV for >8 years. Markers studied included CD4+ cell number, flow cytometric measurements of CD8+ cell expression of CD38 and HLA-DR antigens, and serum markers of immune activation including neopterin, beta2-microglobulin, soluble interleukin-2 receptor, soluble CD8, and soluble tumor necrosis factor receptor-alpha (TNF-alpha) type II. Cox proportional hazards models indicated that elevated CD38 on CD8, a flow cytometric measurement of CD8+ T-lymphocyte activation, was the most predictive marker of those studied for development of a clinical AIDS diagnosis and death. As compared with the reference group, who had CD38 on CD8 <2470 molecules per CD8+ cell and in whom 4 of 99 developed clinical AIDS within 3 years, participants with CD38 on CD8 between 2470 and 3899, 3900 and 7250, and >7250 had relative risks (and numbers developing AIDS within 3 years) of 5.0 (15 of 81), 12.3 (24 of 60), and 41.4 (36 of 49), respectively. The strong prognostic value of CD38 on CD8 measurements and the fundamental importance of chronic immune activation in the pathogenesis of HIV disease suggests that this marker might have utility in the clinical management of HIV-infected persons.

Preferential replication of HIV-1 in the CD45RO memory cell subset of primary CD4 lymphocytes in vitro

The ability of HIV-1 to establish an infection and replicate to high copy number in CD4 lymphocytes is dependent on both the activation state of the cell and virus-encoded regulatory proteins that modulate viral gene expression. To study these required virus-cell interactions, we have used an in vitro cell model of acute HIV infection of quiescent, primary CD4 lymphocytes and subsequent induction of T cell activation and virus replication by lectin or CD3 receptor cross-linking. Experiments were done to determine if the capacity of HIV to establish infection and complete replication was impacted by the maturational state of the CD4 cell target or the specific signal induction pathway engaged during activation. Primary CD4 cells were FACS-sorted into the major phenotypic subsets representative of memory (CD45RO) and naive (CD45RA) cells. Levels of virus replication were compared between infection with wild-type NL4-3 virus and an isogenic mutant containing a deletion in nef regulatory gene. PHA mitogen stimulation was compared with anti-CD3, with and without anti-CD28 costimulation, for induction of cell proliferation and virus replication. In both infected and uninfected cells, the RA cell subset exhibited significantly greater response to CD3/CD28 stimulation than did the RO cell subset. In contrast, the majority of virus replication occurred consistently in the RO cell subset. Deletion of HIV nef function caused a severe reduction in viral replication, especially in the RA naive cell subset after CD3 induction. PCR analysis of viral DNA formation, during infection of quiescent cells, demonstrated that the observed differences in HIV replication capacity between RO and RA cell subsets were not due to inherent differences in cell susceptibility to infection. Our results indicate that HIV replication is enhanced selectively in CD45RO memory phenotype cells through the probable contribution of specialized cellular factors which are produced during CD3-initiated signal transduction.

CD69 expression reliably predicts the anti-CD3-induced proliferative response of lymphocytes from human immunodeficiency virus type 1-infected patients

Published studies suggest that mitogenic responses of lymphocytes can be reliably assessed by monitoring the expression of lymphocyte surface CD69 after 24 h of culture with the stimulant. We tested this hypothesis by determining the ability of lymphocyte CD69 expression to predict the outcome (normal or abnormal) of lymphocyte proliferative responses to anti-CD3 in a group of human immunodeficiency virus type 1 (HIV-1)-infected patients (n = 47). Cutoff values for defining normal and abnormal CD69 expression and proliferative ([3H]thymidine incorporation) responses were established with lymphocytes from healthy uninfected controls (n = 20). Lymphocytes from 29 HIV-infected patients exhibited an abnormal proliferative response, and those from 25 of the 29 also exhibited abnormal CD69 expression (sensitivity, 86.2%). Similarly, lymphocytes from 18 HIV-infected patients exhibited a normal proliferative response, and those from 16 of the 18 also exhibited normal CD69 expression (specificity, 88.9%). The predictive value of a normal CD69 result was 80%, and the predictive value of an abnormal CD69 result was 92.6%. These findings demonstrate that HIV-1-associated impairments in lymphocyte activation can be reliably detected by the rapid and nonradioactive CD69 expression assay.

How many gated lymphocytes are needed for accurate assessment of T-subset percentages by flow cytometry?

Current regulatory agencies specify the use of 2,500 gated lymphocytes for accurate lymphocyte immunophenotyping by flow cytometry. However, acquisition of 2,500 gated lymphocytes is often technically infeasible when testing whole blood from lymphopenic patients. Our laboratory thus compared CD3, CD4, and CD8 percentages obtained from a lymphocyte acquisition gate of 2,500 events with those obtained, respectively, from 1,000 and 500 event acquisition gates. The study group consisted of 59 specimens with CD4 values ranging from 1% to 66%; for data analysis purposes, the group was considered as a whole and was then subdivided according to CD4 percentage (> 25%, < 25%, < 5%). For all groupings analyzed, percentages of CD3+, CD4+, and CD8+ lymphocytes were not significantly different for either 1,000-event or 500-event gates when compared to the standard 2,500 gate (paired t-test). Replicate parallel analyses of some samples indicated that comparable precision is obtained by using the alternative gates. These findings indicate that the use of smaller numbers of acquired lymphocytes is a reasonable alternative in situations where 2,500 lymphocytes cannot be attained.

Costimulatory effects of T cell proliferation during infection with human T lymphotropic virus types I and II are mediated through CD80 and CD86 ligands

The modulation of expression of CD80 and CD86 on T cells following infection with human T lymphotropic virus (HTLV)-I/II and its functional importance in T-T cell interactions was examined. Infection with HTLV-I/II leads to constitutive expression of CD80 and CD86, concomitant to down-modulation of CD28 on T cells. The CD80/CD86+ HTLV-infected T cells stimulated proliferation of allogeneic and autologous resting T cells, which could be specifically blocked by a soluble CTLA-4Ig chimeric protein, anti-CD80 or anti-CD86, but not by anti-CD54. It was necessary to inhibit interaction with both ligands (CD80 and CD86) to optimally block HTLV-mediated proliferation of allogeneic and autologous resting T cells. Simultaneous addition of anti-CD8O and anti-CD86 Abs also inhibited production of IFN-gamma, TNF-alpha, and IL-4, with no effect on IL-10 production, for both allo- and autologous T cell proliferation. Further, there was a direct correlation between the spontaneous proliferation of lymphocytes from patients infected with HTLV-II and expression of CD80, which could be blocked by simultaneous addition of anti-CD80 and anti-CD86. Taken together, these results suggest that HTLV-infected CD80/CD86+ T cells serve as APCs, leading to a sustained proliferation of T cells, and that both ligands participate in allostimulation, autologous proliferation, as well as spontaneous proliferation of HTLV-II-infected PBMC.