Does Paging Clinicians about Tick-Borne Disease Serological Results Impact Clinical Care? A Retrospective Analysis of 70 Cases in North Carolina

Delayed treatment of Rocky Mountain spotted fever is associated with increased morbidity and mortality. Because the diagnosis cannot be established from a single serological test, guidelines recommend empirical antibiotic initiation in suspect patients. We evaluated a policy used by UNC Health of paging clinicians when acute testing for Rickettsia returned with a titer ≥1:256. Our objective was to assess the potential effect of paging on routine treatment practices. Notably, we found that a high proportion of cases (N = 28, 40%) were not prescribed antibiotics until the results were available. The vast majority of these cases did not have evidence of compatible symptoms or disease progression. These findings suggest that paging may have prompted unnecessary treatment. Overall, the policy, which has now been discontinued, appears to have had limited benefit. Efforts are urgently needed to improve adherence to testing and treatment guidelines.

Evaluation of the VioOne HIV profile supplemental assay

HIV is an ongoing global epidemic with estimates of more than a million new infections occurring annually. To combat viral spread, continuous innovations in areas including testing and treatment are necessary. In the United States, the Centers for Disease Control and Prevention recommend that laboratories follow an HIV testing algorithm that first uses a US Food and Drug Administration approved immunoassay to detect antibodies to HIV-1 or HIV-2 as well as HIV-1 p24 antigen in serum or plasma samples. An initially reactive specimen is tested by a supplemental assay for confirmation and to differentiate antibodies to HIV-1 or HIV-2. There are few Food and Drug Administration (FDA)-approved supplemental differentiation tests currently available. A multicenter investigation was conducted to determine the clinical performance for two independent versions of the Avioq VioOne HIV Profile Supplemental Assay (Avioq, Inc., Research Triangle Park, NC). The performance of both assay versions compared favorably with the performance parameters for the Geenius HIV 1/2 Supplemental Assay as published in that assay package insert (Bio-Rad Laboratories, Hercules, CA), the current gold standard for HIV supplemental testing. When comparing the two VioOne assays, version 2 (lacking HIV-2 p27 antibody detection) demonstrated improved reproducibility, specificity, and sensitivity as compared to its predecessor. IMPORTANCE We evaluated the reproducibility, sensitivity, and specificity data for two versions of the VioOne HIV Profile Supplemental Assay and compared these results back to similar results for the Geenius HIV 1/2 Supplemental Assay that are publicly available. Our study concluded that the VioOne HIV Profile Supplemental Assay compared favorably with the Geenius HIV 1/2 Supplemental Assay, thus providing an additional option for clinical laboratories to improve and expand their HIV testing capabilities.

Diplomate in Medical Laboratory Immunology Certification Examination: A New Chapter for Medical Laboratory Immunology

It is indeed a privilege to be an immunologist in what is arguably the golden age of immunology. From astounding advances in fundamental knowledge to groundbreaking immunotherapeutic offerings, immunology has carved out an enviable niche for itself in basic science and clinical medicine. The need and the vital importance of appropriate education, training, and certification in clinical immunology was recognized by the World Health Organization as far back as 1972. In the United States, Ph.D. scientists with board certification in medical laboratory immunology have served as directors of high-complexity Clinical Laboratory Improvement Amendments- and College of American Pathologists-certified clinical immunology laboratories since 1977. From 1977 to 2017, board certification for medical laboratory immunology was administered by the American Society for Microbiology through the American Board of Medical Laboratory Immunology examination. The American Board of Medical Laboratory Immunology examination was phased out in 2017, and in the fall of 2019, the American Society for Clinical Pathology (ASCP) Board of Certification (BOC) examination committee took on the responsibility of developing a new doctoral-level certification examination for medical laboratory immunology. This transition to the ASCP BOC represents a well-deserved and much-needed recognition of the rapid advances in and the highly specialized nature of medical laboratory immunology and its ever-increasing relevance to patient care. This new ASCP BOC certification is called the Diplomate in Medical Laboratory Immunology, and, as of April 1, 2023, it is now available to potential examinees. In this report, we describe the examination, eligibility routes, and potential career pathways for successful diplomates.

Indeterminate QuantiFERON Gold Plus Results Reveal Deficient Interferon Gamma Responses in Severely Ill COVID-19 Patients

SARS-CoV-2 is a novel positive-sense single-stranded RNA virus that has caused a recent pandemic. Most patients have a mild disease course, while approximately 20% have moderate to severe disease, often requiring hospitalization and, in some cases, care in the intensive care unit. By investigating a perceived increased rate of indeterminate QuantiFERON-TB Gold Plus results in hospitalized COVID patients, we demonstrate that severely ill COVID-19 patients have at least a 6-fold reduction of interferon gamma (IFN-γ) levels compared to control patients. What is more, over 60% of these severely ill COVID-19 patients' peripheral T cells were found to be unable to produce measurable IFN-γ when stimulated with phytohemagglutinin (PHA), a potent IFN-γ mitogen, reflected by an indeterminate QuantiFERON-TB Gold Plus result. This defect of IFN-γ production was independent of absolute lymphocyte counts and immunosuppressive therapy. It was associated with increased levels of interleukin-6 (IL-6), which was a predictor of patient outcomes for our cohort when measured early in the course of disease. Finally, in a subset of COVID-19 patients, we found elevated IL-10 levels in addition to IL-6 elevation. In addition to finding a significant limitation of interferon-gamma release assay (IGRA) testing in severely ill COVID-19 patients, these data provide evidence that many of these patients demonstrate a focused Th2 immune response with inhibition of IFN-γ signaling and, in many cases, significant elevations of IL-6.

Next-generation sequencing and clinical histocompatibility testing

Histocompatibility testing is essential for donor identification and risk assessment in solid organ and hematopoietic stem cell transplant. Additionally, it is useful for identifying donor specific alleles for monitoring donor specific antibodies in post-transplant patients. Next-generation sequence (NGS) based human leukocyte antigen (HLA) typing has improved many aspects of histocompatibility testing in hematopoietic stem cell and solid organ transplant. HLA disease association testing and research has also benefited from the advent of NGS technologies. In this review we discuss the current impact and future applications of NGS typing on clinical histocompatibility testing for transplant and non-transplant purposes.

Rapid analysis of local data to inform off-label tocilizumab use early in the COVID-19 pandemic

The interleukin-6 receptor antagonist tocilizumab became widely used early in the coronavirus disease 2019 (COVID-19) pandemic based on small observational studies that suggested clinical benefit in COVID-19 patients with a hyperinflammatory state. To inform our local treatment algorithms in the absence of randomized clinical trial results, we performed a rapid analysis of the first 11 hospitalized COVID-19 patients treated with tocilizumab at our academic medical center. We report their early clinical outcomes and describe the process by which we assembled a team of diverse trainees and stakeholders to extract, analyze, and disseminate data during a time of clinical uncertainty.

Abrogating biologics interference in flow cytometric crossmatching

The flow cytometric crossmatch is currently the gold standard for evaluating donor and recipient histocompatibility. The assay however does have limitations and is sensitive to false positive reactions resulting from the presence of non-HLA antibodies or therapy related immune biologics. Such false positive reactions can lead to the inappropriate decline of an acceptable donor organ or unnecessary therapeutic intervention. Here we describe the successful validation of anti-idiotype blocking antibodies in prevention of false positive flow crossmatch results caused by biologic therapy. Blocking antibodies specific for the Fab portion of Rituximab and/or Alemtuzumab were incubated with biologic containing patient serum prior to use in flow cytometric crossmatching. Biologic blocking successfully negated false positive crossmatch results with Rituximab (B cell ave. % change = -97%) or Alemtuzumab (T cell ave. % change = -99%, B cell ave. % change = -95%) infused sera respectively. Simultaneous blocking of these biologics was also successful. A complex case is presented to demonstrate the application of this procedure.

Highlights of the 33rd annual scientific meeting of the Association of Medical Laboratory Immunologists (AMLI)

The annual meeting of the Association of Medical Laboratory Immunologists (AMLI) was convened virtually over the month of August. Prior to the emergence of the COVID-19 pandemic, AMLI's scientific committee had chosen the following topics as the focus of its 2020 meeting: Histocompatibility Testing and Transplant Immunology; Secondary Immunodeficiency and Immunotherapy Monitoring; ANA Update; and Emerging Infectious Diseases and New Algorithms for Testing. Given the central role of the discipline in the evaluation of the host response to infection, it was apt to add a separate session on antibody testing for SARS-CoV-2 infections to the original program. The current report provides an overview of the subjects discussed in the course of this meeting.

SARS-CoV-2 Seroprevalence among a Southern U.S. Population Indicates Limited Asymptomatic Spread under Physical Distancing Measures

Characterizing the asymptomatic spread of SARS-CoV-2 is important for understanding the COVID-19 pandemic. This study was aimed at determining asymptomatic spread of SARS-CoV-2 in a suburban, Southern U.S. population during a period of state restrictions and physical distancing mandates. This is one of the first published seroprevalence studies from North Carolina and included multicenter, primary care, and emergency care facilities serving a low-density, suburban and rural population since description of the North Carolina state index case introducing the SARS-CoV-2 respiratory pathogen to this population. To estimate point seroprevalence of SARS-CoV-2 among asymptomatic individuals over time, two cohort studies were examined. The first cohort study, named ScreenNC, was comprised of outpatient clinics, and the second cohort study, named ScreenNC2, was comprised of inpatients unrelated to COVID-19. Asymptomatic infection by SARS-CoV-2 (with no clinical symptoms) was examined using an Emergency Use Authorization (EUA)-approved antibody test (Abbott) for the presence of SARS-CoV-2 IgG. This assay as performed under CLIA had a reported specificity/sensitivity of 100%/99.6%. ScreenNC identified 24 out of 2,973 (0.8%) positive individuals among asymptomatic participants accessing health care during 28 April to 19 June 2020, which was increasing over time. A separate cohort, ScreenNC2, sampled from 3 March to 4 June 2020, identified 10 out of 1,449 (0.7%) positive participants.IMPORTANCE This study suggests limited but accelerating asymptomatic spread of SARS-CoV-2. Asymptomatic infections, like symptomatic infections, disproportionately affected vulnerable communities in this population, and seroprevalence was higher in African American participants than in White participants. The low, overall prevalence may reflect the success of shelter-in-place mandates at the time this study was performed and of maintaining effective physical distancing practices among suburban populations. Under these public health measures and aggressive case finding, outbreak clusters did not spread into the general population.

Two cases of asymptomatic massive fetomaternal hemorrhage

Evaluation of fetomaternal hemorrhage (FMH) in the immediate postpartum period is critical for the timely administration of Rh immunoglobulin (RhIG) prophylaxis to minimize the risk of alloimmunization in D-negative mothers of D-positive newborns. We report a series of two clinically-unsuspected cases of massive FMHs identified at our university medical center. Retrospective records of two cases of massive FMH were investigated using the electronic medical record. After positive fetal bleed screens, flow cytometric analysis for hemoglobin F was performed to quantify the volume of the hemorrhages in both cases. Flow cytometric enumeration with anti-D was also performed in one case. The two patients had 209.5 and 75 mL of fetal blood in circulation, resulting in 8 and 4 doses of RhIG administered, respectively. For the former patient, flow cytometric analysis with anti-D ruled out hereditary persistence of fetal hemoglobin and supported the fetal origin of the red cells. Due to the clinically-silent nature of both hemorrhages, further evaluation of the newborns' blood was not performed. These cases highlight the importance of rapidly obtaining accurate measurements of fetal blood loss via flow cytometric analysis in cases of FMH, particularly in clinically-unsuspected cases, to ensure timely administration of adequate immunoprophylaxis to D-negative mothers.

Clinical laboratory immunology: an indispensable player in laboratory medicine

OBJECTIVES

Clinical laboratory immunology affects practically every aspect of medicine. Accordingly, appropriately trained, board-certified clinical laboratory immunologists are key contributors to the diagnosis and management of patients with various immune-mediated conditions. This review highlights the availability of postdoctoral level training programs for clinical laboratory immunology and identifies possible career tracks.

METHODS

Fundamental elements for doctoral level clinical laboratory immunologists are identified and the critical components of diagnostic immunology training as well as career opportunities in and out of academia are described.

RESULTS

Relative to other disciplines in laboratory medicine, little emphasis has been given to clinical laboratory immunology in medical, graduate, and postgraduate training. Formal postgraduate fellowship programs and board certification examinations are available, yet there remains a significant lack of awareness in the medical education community about the value and necessity of training in this field.

CONCLUSIONS

It is anticipated that sharing this knowledge will increase awareness of the discipline of clinical laboratory immunology at the postdoctoral level with implications for the practice of laboratory medicine.

Comparison of the Gen-Probe Aptima HIV-1 and Abbott HIV-1 qualitative assays with the Roche Amplicor HIV-1 DNA assay for early infant diagnosis using dried blood spots

BACKGROUND

The current gold standard for infant diagnosis of HIV-1 is the Roche Amplicor Qualitative DNA assay, but it is being phased out.

OBJECTIVE

Compare the Abbott qualitative assay and the Gen-Probe Aptima assay to the gold standard Roche DNA assay using dried blood spots (DBS).

STUDY DESIGN

The Gen-Probe Aptima and Abbott qualitative HIV-1 assays were compared to the Roche DNA assay for early infant diagnosis. Specificity and sensitivity were determined for the three assays using DBS from 50 HIV-exposed uninfected infants and 269 HIV-1 infected adults from North Carolina, respectively. All of the negative and 151 of the positive DBS had valid results on the 3 different assays, and an additional 118 positive DBS had valid results on the Roche DNA and Aptima assays.

RESULTS

All three assays were very specific. The Roche DNA assay was the most sensitive (96.7%) over a wide range of HIV PVL, including samples with PVL<400 copies/ml. Restricted to samples with PVL>400 copies/ml, the Gen-Probe Aptima assay had sensitivity (96.5%) comparable to the Roche DNA assay (98.8%). The Abbott Qualitative assay was the least sensitive and only had sensitivity above 95% among samples with PVL over 1000 copies/ml.

CONCLUSIONS

The Abbott HIV-1 Qualitative assay was not as sensitive as the comparator assays, so it would not be a useful replacement assay, especially for infants taking antiretroviral prophylaxis. The Gen-Probe Aptima assay is an adequate replacement option for infant diagnosis using DBS.

Residual plasma viraemia and infectious HIV-1 recovery from resting memory CD4 cells in patients on antiretroviral therapy: results from ACTG A5173

BACKGROUND

In HIV-1-infected patients receiving antiretroviral therapy (ART), the relationship between residual viraemia and ex vivo recovery of infectious virus from latently infected CD4 cells is uncertain.

METHODS

We measured residual viraemia (HIV-1 RNA copies/ml) by single-copy assay (SCA) and the latent reservoir by infectious virus recovery from resting memory CD4 cells (infectious units per million cells [IUPM]) in patients who initiated ART. We assessed immune activation by measuring CD38 expression on T-cells.

RESULTS

Ten patients who initiated ART and maintained a plasma HIV-1 RNA level < 200 copies/ml had residual viraemia and IUPM measured every 24 weeks. Five of 10 patients had longitudinal IUPM measured at weeks 24-96; the remainder had IUPM measured 1-3 times over 24-72 weeks. Analyses of 29 paired measurements revealed a positive association between level of residual viraemia and IUPM (0.56 higher log10 HIV-1 RNA copies/ml per 1 log10 higher IUPM; P = 0.005). Residual viraemia level was positively associated with CD38 density and percentage on CD8+ T-cells in concurrent samples and with pre-ART HIV-1 RNA levels.

CONCLUSIONS

In patients with HIV-1 RNA levels < 200 copies/ml 24-96 weeks after initiating ART, the level of viraemia is positively associated with infectious virus recovery from resting memory CD4 cells. Whether this association persists after longer-term suppressive ART needs to be determined. If additional studies show that residual viraemia measured by SCA reflects the size of the latent reservoir in patients who have had virological suppression for longer periods of time, this could facilitate testing of potentially curative strategies to reduce this important reservoir.

Massive CD8 T cell response to primary HIV infection in the setting of severe clinical presentation

Acute HIV-1 infection causes a rapid total body depletion of CD4(+) T cells in most individuals and HIV-1-specific CD8(+) T cell expansion in response to viral replication. A numerically high CD8 T cell response may indicate limited T cell repertoire against HIV and rapid progression. We present a detailed evaluation of an acutely infected individual with a strong HIV-1-specific CD8 T cell response targeting multiple epitopes demonstrating that the upper limit of CD8 expansion in this setting may be much higher than previously reported and was likely driven by the narrow HIV-specific response.

Prospective study of the ARCHITECTHIV Ag/Ab Combo fourth generation assay to detect HIV infection in sexually transmitted infection clinics

This prospective, cross-sectional study of HIV testing at two sexually transmitted infection clinics compares testing results from the ARCHITECT HIV Ag/Ab Combo fourth generation assay against the current standard of care in North Carolina (third generation enzyme immunoassay testing with western blot confirmation and reflex nucleic acid amplification testing of pooled seronegative samples). In this setting, the assay reported a sensitivity of 100%, a specificity of 99.9%, and a median turn-around time of 26.1 h.

DRB1*15 allele is a risk factor for PR3-ANCA disease in African Americans

Anti-neutrophil cytoplasmic autoantibody (ANCA) disease rarely occurs in African Americans and risk factors for the disease in this population are unknown. Here, we genotyped MHC class II alleles and found that, among African Americans, those with proteinase 3-ANCA (PR3-ANCA) had 73.3-fold higher odds of having HLA-DRB1*15 alleles than community-based controls (OR 73.3; 95% CI 9.1 to 591). In addition, a disproportionate number of African American patients carried the DRB1*1501 allelic variant of Caucasian descent rather than the DRB1*1503 allelic variant of African descent. Among Caucasians, those with PR3-ANCA had 2.2-fold higher odds of carrying DRB1*1501 than controls (OR 2.2; 95% CI 1.2 to 4.0). A validation study supported by the Vasculitis Clinical Research Consortium confirmed the strong association between the DRB1*15 allele and PR3-ANCA disease, among African Americans. Furthermore, we found that DRB1*1501 protein binds with high affinity to amino acid sequences of sense-PR3, purportedly an antigenic epitope, and to the amino acid sequence complementary to this epitope in vitro. Peptides of sense-PR3 and complementary-PR3 also bound to TNF-α-induced surface expression of DRB1*1501 on peripheral neutrophils. Taken together, these data suggest HLA-DRB1*15 alleles contribute to the pathogenesis of PR3-ANCA disease.

ANCA patients have T cells responsive to complementary PR-3 antigen

Some patients with proteinase 3 specific anti-neutrophil cytoplasmic autoantibodies (PR3-ANCA) also have antibodies that react to complementary-PR3 (cPR3), a protein encoded by the antisense RNA of the PR3 gene. To study whether patients with anti-cPR3 antibodies have cPR3-responsive memory T cells we selected conditions that allowed cultivation of memory cells but not naïve cells. About half of the patients were found to have CD4+TH1 memory cells responsive to the cPR3(138-169)-peptide; while only a third of the patients had HI-PR3 protein responsive T cells. A significant number of T cells from patients responded to cPR3(138-169) peptide and to HI-PR3 protein by proliferation and/or secretion of IFN-gamma, compared to healthy controls while there was no response to scrambled peptide. Cells responsive to cPR3(138-169)-peptide were not detected in MPO-ANCA patients suggesting that this response is specific. The HLADRB1(*) 15 allele was significantly overrepresented in our patient group and is predicted to bind cPR3(138-169) peptide with high affinity. Regression analysis showed a significant likelihood that anti-cPR3 antibodies and cPR3-specific T cells coexist in individuals, consistent with an immunological history of encounter with a PR3-complementary protein. We suggest that the presence of cells reacting to potential complementary protein pairs might provide an alternative mechanism for auto-immune diseases.

Isolated donor specific alloantibody-mediated rejection after ABO compatible liver transplantation

Antibody-mediated rejection (AMR) after liver transplantation is recognized in ABO incompatible and xeno-transplantation, but its role after ABO compatible liver transplantation is controversial. We report a case of ABO compatible liver transplantation that demonstrated clinical, serological and histological signs of AMR without evidence of concurrent acute cellular rejection. AMR with persistently high titers of circulating donor specific antibodies resulted in graft injury with initial centrilobular hepatocyte necrosis, fibroedematous portal expansion mimicking biliary tract outflow obstruction, ultimately resulting in extensive bridging fibrosis. Immunofluorescence microscopy demonstrated persistent, diffuse linear C4d deposits along sinusoids and central veins. Despite intense therapeutic intervention including plasmapheresis, IVIG and rituximab, AMR led to graft failure. We present evidence that an antibody-mediated alloresponse to an ABO compatible liver graft can cause significant graft injury independent of acute cellular rejection. AMR shows distinct histologic changes including a characteristic staining profile for C4d.

A pilot study evaluating time to CD4 T-cell count <350 cells/mm(3) after treatment interruption following antiretroviral therapy +/- interleukin 2: results of ACTG A5102

BACKGROUND

Although an intermittent antiviral treatment (ART) strategy may limit long-term toxicity and cost, there is concern about the risk for virologic failure, selection of drug resistance mutations, and disease progression. By boosting CD4 T-cell counts, interleukin 2 (IL-2) could safely prolong the duration of treatment interruption (TI) in a CD4-driven strategy.

METHODS

The AIDS Clinical Trials Group (ACTG) study A5102 evaluated 3 cycles of IL-2 before TI, on clinical and immunologic outcomes, using a CD4 T-cell count of <350 cells/mm as the threshold for restarting ART. Forty-seven HIV-infected subjects on potent ART with CD4 T-cell counts of > or =500 cells/mm or more and HIV RNA levels of less than 200 copies/mL were randomized to arm A (ART + three 5-day cycles of IL-2 at 4.5 million U, Sc, BID every 8 weeks, n = 23) or arm B (ART alone, n = 24) for 18 weeks (step 1). At the end of step 1, subjects with a CD4 T-cell count of > or =500 cells/mm or more stopped ART until a CD4 count of <350 cells/mm (step 2). CD4 T-cell count, time to return of viremia, and the emergence of drug resistance mutations after TI were compared between study arms.

RESULTS

IL-2 recipients maintained higher CD4 counts during TI for 48 weeks with a waning of the CD4 effect by 72 weeks. A sustained CD4 T-cell count of more than 350 cells/mm and more durable TI were associated with a higher nadir CD4 T-cell count before ART and higher naive CD4 T-cell count at entry. After TI, a higher viral set point and drug resistance mutations at virologic rebound were associated with a shorter time to CD4 T-cell count of less than 350 cell/mm. There were no differences in the magnitude of virologic rebound (at week 8 of step 2, median log10 HIV RNA level was 4.23 for arm A and 4.21 for arm B) or the steady-state HIV-1 RNA level after week 8.

CONCLUSIONS

IL-2 before TI did not prolong time to CD4 of less than 350 cells/mm. A TI strategy utilizing a CD4 T-cell threshold of less than 350 cells/mm for restarting ART appears generally safe with most subjects in both arms remaining off ART for more than 1 year. Implications of our results for TI strategies include the potential advantage of starting ART at higher CD4 T-cell levels while avoiding any drug resistance and evaluating immunomodulators or drugs to reduce T-cell activation and HIV-1 RNA rebound during the TI.

Prevalence of HIV infection among young adults in the United States: results from the Add Health study

OBJECTIVES

We estimated HIV prevalence rates among young adults in the United States.

METHODS

We used survey data from the third wave of the National Longitudinal Study of Adolescent Health, a random sample of nearly 19000 young adults initiated in 1994-1995. Consenting respondents were screened for the presence of antibodies to HIV-1 in oral mucosal transudate specimens. We calculated prevalence rates, accounting for survey design, response rates, and test performance.

RESULTS

Among the 13184 participants, the HIV prevalence rate was 1.0 per 1000 (95% confidence interval [CI] = 0.4, 1.7). Gender-specific prevalence rates were similar, but rates differed markedly between non-Hispanic Blacks (4.9 per 1000; 95% CI=1.8, 8.7) and members of other racial/ethnic groups (0.22 per 1000; 95% CI=0.00, 0.64).

CONCLUSIONS

Racial disparities in HIV in the United States are established early in the life span, and our data suggest that 15% to 30% of all cases of HIV occur among individuals younger than 25 years.

The Prevalence of Trichomoniasis in Young Adults in the United States

BACKGROUND AND OBJECTIVES

The prevalence of trichomoniasis in the general population of the United States is unknown. This study provides the first population-based prevalence estimates of trichomoniasis among young adults in the United States.

METHODS

The National Longitudinal Study of Adolescent Health (Add Health) is an ongoing prospective cohort study. In a cross-sectional analysis of Wave III of Add Health (N = 12,449), we determined the prevalence of trichomoniasis using a polymerase chain reaction assay.

RESULTS

The estimated overall prevalence of trichomoniasis in U.S. young adults was 2.3% (95% confidence interval [CI], 1.8-2.7%). The prevalence was slightly higher among women (2.8%; 95% CI, 2.2-3.6%) than men (1.7%; 95% CI, 1.3-2.2%). The prevalence increased with age and varied by region, with the south having the highest prevalence (2.8%; 95% CI, 2.2-3.5%). The prevalence was highest among black women (10.5%; 95% CI, 8.3-13.3%) and lowest among white women (1.1%; 95% CI, 0.8-1.6%). Among men, the prevalence was highest among Native Americans (4.1%; 95% CI, 0.4-29.3%) and blacks (3.3%; 95% CI, 2.2-4.9%), and lowest among white men (1.3%; 95% CI, 0.9-1.8%).

CONCLUSIONS

Trichomoniasis is moderately prevalent among the general U.S. population of young adults and disturbingly high among certain racial/ethnic groups.

Practical evaluation of methods for detection and specificity of autoantibodies to extractable nuclear antigens

Detection and specificity of autoantibodies against extractable nuclear antigens (ENA) play a critical role in the diagnosis and management of autoimmune disease. Historically, the detection of these antibodies has employed double immunodiffusion (DID). Autoantibody specificity was correlated with diagnoses by this technique. Enzyme immunoassays have been developed by multiple manufacturers to detect and identify the specificity ENA autoantibodies. To address the relationship of ENA detection by DID and enzyme immunoassay, the performances of five immunoassays were compared. These included two DID and three enzyme-linked immunoassays (ELISA) (both screening and individual antigen profile kits). The sample set included 83 ENA-positive, antinuclear-antibody (ANA)-positive specimens, 77 ENA-negative, ANA-positive specimens, and 20 ENA- and ANA-negative specimens. Sensitivity and specificity were calculated by two methods: first, by using the in-house DID result as the reference standard, and second, by using latent class analysis, which evaluates each kit result independently. Overall, the results showed that the ELISA methods were more sensitive for detection of ENA autoantibodies than DID techniques, but presence and/or specific type of ENA autoantibody did not always correlate with the patient's clinical presentation. Regardless of the testing strategy an individual laboratory uses, clear communication with the clinical staff regarding the significance of a positive result is imperative. The laboratory and the clinician must both be aware of the sensitivity and specificity of each testing method in use in the clinical laboratory.

Prevalence of chlamydial and gonococcal infections among young adults in the United States

CONTEXT

Chlamydial and gonococcal infections are important causes of pelvic inflammatory disease, ectopic pregnancy, and infertility. Although screening for Chlamydia trachomatis is widely recommended among young adult women, little information is available regarding the prevalence of chlamydial and gonococcal infections in the general young adult population.

OBJECTIVE

To determine the prevalence of chlamydial and gonococcal infections in a nationally representative sample of young adults living in the United States.

DESIGN, SETTING, AND PARTICIPANTS

Cross-sectional analyses of a prospective cohort study of a nationally representative sample of 14,322 young adults aged 18 to 26 years. In-home interviews were conducted across the United States for Wave III of The National Longitudinal Study of Adolescent Health (Add Health) from April 2, 2001, to May 9, 2002. This study sample represented 66.3% of the original 18,924 participants in Wave I of Add Health. First-void urine specimens using ligase chain reaction assay were available for 12,548 (87.6%) of the Wave III participants.

MAIN OUTCOME MEASURES

Prevalences of chlamydial and gonococcal infections in the general young adult population, and by age, self-reported race/ethnicity, and geographic region of current residence.

RESULTS

Overall prevalence of chlamydial infection was 4.19% (95% confidence interval [CI], 3.48%-4.90%). Women (4.74%; 95% CI, 3.93%-5.71%) were more likely to be infected than men (3.67%; 95% CI, 2.93%-4.58%; prevalence ratio, 1.29; 95% CI, 1.03-1.63). The prevalence of chlamydial infection was highest among black women (13.95%; 95% CI, 11.25%-17.18%) and black men (11.12%; 95% CI, 8.51%-14.42%); lowest prevalences were among Asian men (1.14%; 95% CI, 0.40%-3.21%), white men (1.38%; 95% CI, 0.93%-2.03%), and white women (2.52%; 95% CI, 1.90%-3.34%). Prevalence of chlamydial infection was highest in the south (5.39%; 95% CI, 4.24%-6.83%) and lowest in the northeast (2.39%; 95% CI, 1.56%-3.65%). Overall prevalence of gonorrhea was 0.43% (95% CI, 0.29%-0.63%). Among black men and women, the prevalence was 2.13% (95% CI, 1.46%-3.10%) and among white young adults, 0.10% (95% CI, 0.03%-0.27%). Prevalence of coinfection with both chlamydial and gonococcal infections was 0.030% (95% CI, 0.18%-0.49%).

CONCLUSIONS

The prevalence of chlamydial infection is high among young adults in the United States. Substantial racial/ethnic disparities are present in the prevalence of both chlamydial and gonococcal infections.

Human leukocyte antigen mismatches predispose to the severity of bronchiolitis obliterans syndrome after lung transplantation

BACKGROUND

Obliterative bronchiolitis (OB) is the most important cause of long-term morbidity and mortality in lung transplant recipients, and probably results from alloimmune airway injury. Bronchiolitis obliterans syndrome (BOS), defined as a staged decline in pulmonary function, is the clinical correlate of OB.

OBJECTIVE

Evaluation of the risk and severity of BOS on the basis of the incompatibility of donor and recipient human leukocyte antigen (HLA) molecules.

DESIGN

Retrospective cohort study.

SETTING

Large university hospital.

PARTICIPANTS

Lung transplant recipients between January 1990 and January 2000.

MEASUREMENTS

We determined the BOS stage using internationally promulgated guidelines with a minor modification on all recipients at their 4-year transplant anniversary. Recipients whose graft function had deteriorated or who died due to causes other than BOS were excluded from the study. HLA loci mismatches and other covariables, including recipient age, donor age, cytomegalovirus (CMV) mismatch, cold ischemic time, use of cardiopulmonary bypass, ventilatory days, episodes of acute rejection and CMV pneumonitis, mean trough cyclosporin A (CsA) level, episodes of subtherapeutic CsA levels, and histopathology of OB and diffuse alveolar damage were entered into the analysis of BOS predictors.

RESULTS

Sixty-four patients met the inclusion and exclusion criteria of the study at the 4-year posttransplant time point. In univariate analyses, the number of combined HLA-A and HLA-B mismatches was strongly associated with the stage of BOS at 4 years (p = 0.002). This association remained significant after the inclusion of other potential risk factors for BOS in multiple linear regression models. Pretransplant and posttransplant proportional odds models confirmed that the increasing number of combined HLA-A and HLA-B mismatches increased the overall severity of BOS (adjusted odds ratio, 1.84 [p = 0.035] vs 1.69 [p = 0.067], respectively). A trend toward significance was seen with HLA-DR mismatching (p = 0.17).

CONCLUSIONS

The degree of HLA class I mismatching between donors and recipients predisposes lung transplant recipients to the development and severity of BOS.

24. Clinical and laboratory assessment of immunity

Clinicians order specific laboratory tests and interpret laboratory data that will be useful in establishing a diagnosis of immunodeficiency, either inherited (primary) immunodeficiencies or acquired (secondary) immunodeficiencies. The clinical immunologic evaluation of patients for immunodeficiency proceeds in an orderly fashion, from screening tests to sophisticated tests. The medical history and physical examination of the patient frequently provide clues guiding the level of entry into this testing program. Specific tests have been designed to screen for the four basic mechanisms of host defense: Antibody, T cell, phagocyte, and complement. The clinical immunology laboratory is a powerful adjunct to the clinician in the initial evaluation of immunodeficiency disorders and in the design of more sophisticated testing for selected patients.

Comparison of human immunodeficiency virus antigens as stimulants for lymphocyte proliferation assays

CD4 proliferative responses to the human immunodeficiency virus (HIV) type 1 (HIV-1) p24 (gag) antigen inversely correlate with the plasma viral load in HIV-infected subjects who control viral replication without antiretroviral therapy. Use of a single HIV-1 protein to assess CD4 proliferative responses may not reflect the global response to this pathogen. We compared the abilities of HIV p24 and gp120 antigens from two different vendors, an inactivated whole HIV-1 MN virion preparation and an HIV-1E culture supernatant antigen, to elicit proliferative responses in HIV-seropositive and HIV-seronegative donors. Peripheral blood mononuclear cells from 12 HIV-seropositive donors (each with HIV-1 loads <4,000 copies/ml of plasma, >350 CD4 T lymphocytes/mm(3), and no antiretroviral therapy) and 15 HIV-seronegative donors were assessed with multiple concentrations of each stimulant by standard lymphocyte proliferation assays. Wide variations in response rates were found, with zero, three, five, and eight individuals demonstrating stimulation indices of >3 for the HIV culture antigen supernatant, gp120, p24, and inactivated whole-virus preparations, respectively. These results suggest that the use of the inactivated whole virus resulted in a more sensitive assay for detection of CD4 T-lymphocyte function in HIV-infected subjects.

Evidence of immune reconstitution in antiretroviral drug-experienced patients with advanced HIV disease

Highly active antiretroviral therapy (HAART) of HIV disease is associated with effective virologic control, immune reconstitution, and clinical improvements. This study addresses the potential for improvements in lymphocyte phenotype and virologic responses of HIV-infected persons with extensive experience with dual nucleoside reverse transcriptase (NRTI) treatment and advanced HIV disease after a change to a potent antiretroviral therapy (NRTI + protease inhibitor). The majority of participants achieved virologic success. There was a median rise in CD4+ lymphocytes of 99 cells/mm(3) by 48 weeks, because of an increase in memory CD4+ cells at 4 and 16 weeks, followed by a later increase in naive CD4+ cells between weeks 16 and 48. The proportion of activated, DR+ CD38+ CD8+ lymphocytes decreased during the 48 weeks of follow-up. The immunologic findings (increased memory and naive T cells and reduced activation levels) were significantly improved in participants with persistent suppression of viral replication over the 48 weeks of the study. Baseline HIV RNA copy number was lower (median, 14,784 copies/ml) in persons who responded virologically than in those not suppressing viral replication (median, 49,454 copies/ml). CD4+ cell counts above the median (125/mm(3)) at time 0 for the participants, was the only baseline immunologic marker significantly associated with viral suppression at week 48. Participants older than 40 years of age demonstrated less immunologic recovery. The results of the study show that patients with extensive experience with NRTIs respond both virologically and immunologically during the first 48 weeks of therapy with a potent antiretroviral regimen.

Clinical utility of measuring white blood cells on vaginal wet mount and endocervical gram stain for the prediction of chlamydial and gonococcal infections

BACKGROUND

White blood cells on endocervical Gram stain and vaginal wet mount are frequently used to predict chlamydial and gonococcal infections. Previous studies provide conflicting evidence for the clinical utility of these tests.

GOAL

To evaluate the clinical utility of measuring white blood cells on vaginal wet mount and endocervical Gram stain for the prediction of chlamydial infection and gonorrhea.

STUDY DESIGN

Women undergoing pelvic examinations at 10 county health department family planning and sexually transmitted disease clinics were tested for chlamydial infection by ligase chain reaction assay (n = 4550) and for gonorrhea by culture (n = 4402). Vaginal wet mount and endocervical Gram stains were performed in county laboratories at the time of examination.

RESULTS

The prevalences of chlamydial infection and gonorrhea were 8.8% and 3.2%, respectively. For detection of chlamydial or gonococcal infection, the likelihood ratio was 2.85 (95% CI, 2.10-3.87) for > 30 white blood cells on vaginal wet mount and 2.91 (95% CI, 2.07-4.09) for > 30 white blood cells on endocervical Gram stain. Similar results were seen for individual diagnoses either of chlamydial infection or of gonorrhea.

CONCLUSION

Vaginal wet mount and endocervical Gram stain white blood cells are useful for the presumptive diagnosis of chlamydial infection or gonorrhea only in settings with a relatively high prevalence of infection or when other predictors can increase the likelihood of infection.

Shipment impairs lymphocyte proliferative responses to microbial antigens

Lymphocyte proliferation assays (LPAs) are widely used to assess T-lymphocyte function of patients with human immunodeficiency virus infection and other primary and secondary immunodeficiency disorders. Since these assays require expertise not readily available at all clinical sites, specimens may be shipped to central labs for testing. We conducted a large multicenter study to evaluate the effects of shipping on assay performance and found significant loss of LPA activity. This may lead to erroneous results for individual subjects and introduce bias into multicenter trials.

Need for an external proficiency testing program for cytokines, chemokines, and plasma markers of immune activation

An external evaluation program for measuring the performance of laboratories testing for cytokines and immune activation markers in biological fluids was developed. Cytokines, chemokines, soluble cytokine receptors, and other soluble markers of immune activation (CSM) were measured in plasma from a healthy human immunodeficiency virus (HIV)-seronegative reference population and from HIV-seropositive individuals as well as in supernatant fluids from in vitro-stimulated human immune cells. The 14 components measured were tumor necrosis factor (TNF) alpha, gamma interferon, interleukin-1 (IL-1), IL-2, IL-4, IL-6, IL-10, Rantes, MIP-Ia, MIP-Ibeta, soluble TNF receptor II, soluble IL-2 receptor alpha, beta(2)-microglobulin, and neopterin. Twelve laboratories associated with the Adult and Pediatric AIDS Clinical Trial Groups participated in the study. The performance features that were evaluated included intralaboratory variability, interlaboratory variability, comparison of reagent sources, and ability to detect CSM in the plasma of normal subjects as well as the changes occurring in disease. The principal findings were as follows: (i) on initial testing, i.e., before participating in the program, laboratories frequently differed markedly in their analytic results; (ii) the quality of testing of a CSM in individual participating laboratories could be assessed; (iii) most commercial kits allowed distinction between normal and abnormal plasma CSM levels and between supernatants of stimulated and unstimulated cells; (iv) different sources of reagents and reference standards frequently provided different absolute values; (v) inexperienced laboratories can benefit from participating in the program; (vi) laboratory performance improved during active participation in the program; and (vii) comparability between analyses conducted at different sites can be ensured by an external proficiency testing program.

Multisite comparison of methods for the quantitation of the surface expression of CD38 on CD8(+) T lymphocytes. The ACTG Advanced Flow Cytometry Focus Group

We evaluated the effect of specimen processing variations and quantitation methods on quantitative determination of CD38 expression on CD8 T lymphocytes. Neither lysing reagent (ammonium chloride versus BD FACSlyse), fixation (paraformaldehyde versus no final fixation step), nor acquisition delay (acquisition within 6 h after fixation versus 24 h after fixation) had a significant effect on CD38 relative fluorescent intensity or CD38 quantitative estimates (RFI or antibodies bound per cell). The only significant difference in fluorescent intensity and CD38 antibodies bound per cell (ABC) was encountered when whole blood was held for 24 h prior to staining and fixation and then acquired after another 24-h hold. However, for all sample processing methods above, the CD4 biologic calibrator and QuantiBRITE bead methods gave significantly different estimates of CD38 intensity. In many cases, however, these differences are relatively small and were more pronounced in certain laboratories. We conclude that there is some flexibility in sample processing methods for quantitative CD38 determination; however, it is preferable for a laboratory to employ one method of fluorescence quantitation calculation consistently because small differences are detected between different methods. Cytometry (Comm. Clin. Cytometry) 42:174-179, 2000.

Features of urethritis in a cohort of male soldiers

Of 400 cases of urethritis in male soldiers enrolled in a behavioral intervention project, the etiology of 69% was defined at study enrollment, as well as the etiology of 72% of 25 repeated episodes involving 21 men during the first 78 days of active follow-up (5% of the cohort). Chlamydia trachomatis (36%), Neisseria gonorrhoeae (34%), and Ureaplasma urealyticum (19%) were the most common causes of infection identified at enrollment and during subsequent visits (44%, 28%, and 12%, respectively). By univariate analysis, patients with repeated infection ("repeaters") were significantly more likely to report a history of sexually transmitted disease (STD; relative risk [RR], 3) and sex with sex workers (RR, 4) than were nonrepeaters. By multivariate analysis, only STD history was significant (RR, 2.8). Characteristics of repeaters in this cohort suggest that specific patterns may be used to establish screening "profiles" of potential repeaters, by which such individuals might be targeted for aggressive intervention at the time of the initial diagnosis.

Selective screening for chlamydial infection: which criteria to use?

BACKGROUND

Screening sexually active women for Chlamydia trachomatis is necessary to detect asymptomatic infections. Selective screening is a common strategy because universal screening is too costly in many settings. In order to guide local programs in the choice of selective screening criteria, we examined the performance of previously proposed screening criteria for C. trachomatis.

METHODS

A clinic-based, cross-sectional study was conducted in public family planning and sexually transmitted disease (STD) clinics in ten counties in North Carolina. Women (n = 4471 in family planning and n = 2201 in STD clinics) undergoing pelvic examination were enrolled consecutively. Nine sets of screening criteria, including age alone, were compared using sensitivity, specificity, number of tests required and receiver-operator characteristic (ROC) analysis. All women underwent testing with ligase chain reaction assay of cervical specimens to identify C trachomatis infection.

RESULTS

The prevalence of C. trachomatis was 7.8% and 11.0% in family planning and STD clinics, respectively. The sensitivities of published criteria ranged from 0.50 to 0.97. Specificities ranged from 0.05 to 0.66. In family planning clinics, the best performing criteria would detect 84% of infections while screening 51% of women. In STD clinics, the same criteria would detect 83% of infections but require testing 67% of women. Testing women aged < or =22 would detect 77% of infections in family planning and 74% of infections in STD clinics, while testing 51% and 48% of the women, respectively.

CONCLUSIONS

When site-specific criteria cannot be developed, age alone is an acceptable strategy for selective screening for chlamydial infection.

Diagnostic usefulness of antineutrophil cytoplasmic autoantibody serology. Comparative evaluation of commercial indirect fluorescent antibody kits and enzyme immunoassay kits

Antineutrophil cytoplasmic autoantibodies (ANCAs) are increasingly used as serologic markers for pauci-immune crescentic glomerulonephritis and small vessel vasculitis. Many hospital laboratories and referral laboratories use commercial assay kits to detect ANCAs, despite inadequate documentation in the medical literature of kit performance. We evaluated the diagnostic sensitivity, specificity, and predictive value of 3 commercial indirect immunofluorescence assay (IFA) kits and 7 commercial enzyme immunoassay (EIA) kits for several ANCA subtypes. Serum samples from 396 patients with a variety of renal diseases were analyzed, including 146 patients with pauci-immune crescentic glomerulo-nephritis with or without systemic vasculitis. With 1 exception, the kits had more than 90% agreement with the reference standard and gave results similar to those of research laboratories. IFA diagnostic sensitivity ranged from 81% to 91% and EIA sensitivity from 75% to 84%. Maximum specificity was obtained with combined IFA and EIA. Diagnostic specificity was more than 70% for 2 of 3 IFA kits and at least 90% for 5 of 7 EIA kits. Predictive values varied with clinical manifestations. Most commercial IFA and EIA kits that were evaluated provide acceptably accurate analytic results.

A whole-blood assay for qualitative and semiquantitative measurements of CD69 surface expression on CD4 and CD8 T lymphocytes using flow cytometry

A whole-blood flow cytometry-based assay was utilized to assess CD4 and CD8 T-lymphocyte activation in response to phytohemagglutinin (PHA) stimulation. T-lymphocyte activation was assessed by qualitative (percent CD69) and semiquantitative (anti-CD69 antibody binding capacity) measurements of CD69 surface expression. Whole-blood samples from 21 healthy and 21 human immunodeficiency virus (HIV)-infected (<500 absolute CD4 counts per mm3) individuals were stimulated with 20 microg of PHA per ml for 18 to 24 h. The proportions of activated CD4 and CD8 T lymphocytes expressing CD69 (percent CD69) and the levels of CD69 expression on each T-lymphocyte subset (anti-CD69 antibody binding capacity) were measured. By using this assay system, T-lymphocyte activation was impaired in both CD4 and CD8 T-lymphocyte subsets of HIV-infected individuals. The proportions of CD69-positive CD4 and CD8 T lymphocytes were 43 and 27% lower, respectively, in samples from HIV-infected individuals compared to samples from healthy individuals. Similarly, the levels of CD69 expression on each activated CD4 and CD8 T-lymphocyte subset were 48 and 51% lower, respectively. These results suggest that both qualitative and semiquantitative measurements of CD69 surface expression by flow cytometry can be used to assess T-lymphocyte activation.

Enumeration of CD34-positive stem cells: evaluation and comparison of three methods

Accurate enumeration of CD34+ stem cells is important in assessing the need for continued mobilization and subsequent apheresis collections. We compared two new analysis systems, ProCOUNT (Becton Dickinson Immunocytometry Systems) and IMAGN 2000 STELLer (Biometric Imaging, Inc.) with our current (3-Color) flow cytometry-based method. The ProCOUNT system uses an absolute counting tube, which contains reference beads and a specific (multiple) gating strategy to determine an absolute count. The STELLer assay combines microvolume fluorimetry and automated analysis software to determine an absolute count. To evaluate linearity and reproducibility, peripheral blood was spiked with CD34+ cells (KG1a cell line). Three dilution series (measured at approximately equal to 0, 5, 10, 25, 50, and 100 CD34+ cells/microliter) were analyzed by each method. Analysis of predicted versus actual CD34+ concentration showed excellent correlation with all methods (r2 > or = 0.97, slope 0.98-1.04). To further assess precision, two PBSC samples, at approximately 200 and 800 CD34+ cells/microliter, respectively, were analyzed 10 times by each method. Coefficients of variation for the precision analysis of these samples were 5.1%-6.4% and 5.4%-12.3%, respectively. To assess overall performance, 75 patient specimens were analyzed. Excellent correlation (r2 values of 0.89-0.98) was observed among all three methods. We conclude that the three methods provide comparable linearity and reproducibility.

Gamma/delta T-cell hepatosplenic lymphoma: review of the literature, diagnosis by flow cytometry and concomitant autoimmune hemolytic anemia

Hepatosplenic gamma/delta T-cell lymphoma is recognized as a subset of peripheral T-cell lymphoma in the REAL classification. Histologically these tumors are characterized by a mixture of small to medium-sized atypical lymphocytes. To date, approximately 15 cases of hepatosplenic gamma delta T-cell lymphoma have been reported. Affected individuals are usually young adults with a median age of 34 years. Patients commonly present with B symptoms and hepatosplenomegaly, but an absence of lymphadenopathy. The disease follows an aggressive course with median survival of 12-14 months and poor response to combination chemotherapy agents. Occasionally, the occurrence of frank blast transformation constitutes a terminal event for the patient. Although cytopenias are relatively common, nonimmune hemolytic anemia has been reported in one patient only. This is the first report of autoimmune hemolytic anemia associated with hepatosplenic gamma delta T-cell lymphoma.

Intensity discrimination as a function of stimulus level with electric stimulation

Difference limens (DLs) for changes in electric current were measured from multiple electrodes in each of eight cochlear-implanted subjects. Stimuli were 200-microseconds/phase biphasic pulse trains delivered at 125 Hz in 300-ms bursts. DLs were measured with an adaptive three-alternative forced-choice procedure. Fixed-level psychometric functions were also obtained in four subjects to validate the adaptive DLs. Relative intensity DLs, specified as Weber fractions in decibels [10 log (delta I/I)] for standards above absolute threshold, decreased as a power function of stimulus intensity relative to absolute threshold [delta I/I = beta (I/I0) alpha] in the same manner as Weber fractions for normal acoustic stimulation reported in previous studies. Exponents (alpha) of the power function for electric stimulation ranged from -0.4 to -3.2, on average, an order of magnitude larger than exponents for acoustic stimulation, which range from -0.07 to -0.11. Normalization of stimulus intensity to the dynamic range of hearing resulted in Weber functions with similar negative slopes for electric and acoustic stimulation, corresponding to an 8-dB average improvement in Weber fractions across the dynamic range. Sensitivity to intensity change ¿10 log beta¿ varied from -0.42 to -13.5 dB compared to +0.60 to -3.34 dB for acoustic stimulation, but on average was better with electric stimulation than with acoustic stimulation. Psychometric functions for intensity discrimination yielded Weber fractions consistent with adaptive procedures and d' was a linear function of delta I. Variability among repeated Weber-fraction estimates was constant across dynamic range. Relatively constant Weber fractions across all or part of the dynamic range, observed in some subjects, were traced to the intensity resolution limits of individual implanted receiver/stimulators. DLs could not be accurately described by constant amplitude changes, expressed as a percentage of dynamic range ¿delta A(% DR)¿. Weber fractions from prelingually deafened subjects were no better or worse than those from postlingually deafened subjects. The cumulative number of discriminable intensity steps across the dynamic range of electric hearing ranged from as few as 6.6 to as many as 45.2. Physiologic factors that may determine important features of electric intensity discrimination are discussed in the context of a simple, qualitative, rate-based model. These factors include the lack of compressive cochlear preprocessing, the relative steepness of neural rate-intensity functions, and individual differences in patterns of neural survival.

Determination of natural killer cell function by flow cytometry

Natural killer cells (NK cells) are a subset of peripheral blood lymphocytes that mediate non-major histocompatibility complex-restricted cytotoxicity of foreign target cells. The "gold standard" assay for NK cell activity has been the chromium release assay. This method is not easily performed in the clinical laboratory because of difficulties with disposal of radioactive and hazardous materials, short reagent half-lives, expense, and difficulties with assay standardization. We describe a flow cytometric assay for the clinical measurement of NK cell activity. This study compared the chromium release assay and the flow cytometric assay by using clinically relevant specimens. There were no significant differences between the two assays in the measurement of lytic activity for 17 peripheral blood specimens or in reproducibility in repeated samplings of healthy individuals. We also established a normal range of values for NK activity in healthy adults and identified a small cluster of individuals who have exceptionally high or low levels of NK activity. The flow cytometric assay was validated by testing specimens from subjects expected to have abnormally low levels of NK activity (pregnant women) and specimens from healthy individuals in whom the activity of NK cells was enhanced by exposure to interleukin-2 or alpha interferon. Treatment with these agents was associated with a significant increase in NK activity. These results confirm and extend those of others, showing that the flow cytometric assay is a viable alternative to the chromium release assay for measuring NK cell activity.

Genital ulcer disease. Management in the HIV era

What are the main causes of genital ulcer disease in the United States? Why is clinical diagnosis so difficult? What role will molecular diagnostics have in the future? The authors answer these questions and provide a functional approach to successful management of three common types of sexually transmitted genital ulcers.