Measurement and interpretation of pneumococcal IgG levels for clinical management

Validation and comprehensive analysis of Streptococcus pneumoniae IgG WHO enzyme-linked immunosorbent assay in an Indian reference laboratory

Monitoring serotype-specific IgG levels against pneumococci is crucial for assessing immunity, vaccine efficacy, and evaluating vaccination programs. The WHO ELISA for pneumococci is a standardized assay ensuring consistency in testing and comparability of results across laboratories. It involves a rigorous testing process to confirm accurate, precise and reliable detection of antibodies. We validated the protocol for 13 pneumococcal serotypes by assessing its specificity, reproducibility (coefficient of variation ≤15%), repeatability (coefficient of variation ≤20%), accuracy, lower limit of quantification, stability, and robustness. We found these parameters were within acceptable ranges and showed excellent performance. Our findings imply that the method employed is appropriate for evaluating 13 valent pneumococcal conjugate vaccine which is introduced in the national immunization program by comparing pre-and post-vaccination IgG response.

Importance of NK Cells in Cellular and Humoral Responses Triggered by Pneumococcus Vaccination

INTRODUCTION

Despite the success of vaccination in reducing overall rate of pneumococcal pneumonia, Streptococcus pneumoniae is still held responsible for high mortality and modality rates worldwide. Our study aimed to investigate the potential role played by NK cells in immune response generated by pneumococcal vaccination, which could contribute to the development of more effective vaccines.

METHODS

The study included mice with and without NK cell depletion which were immunized with pneumococcus polysaccharide-conjugated vaccine followed by pneumococcus polysaccharide vaccine (PPV). Serum samples and splenocytes were collected from mice sacrificed 4 weeks after the last PPV dose. Serum samples were used for antibody level quantification by ELISA assay, while splenocytes were treated with PPV in vitro before monitoring CD4+ T-cell subsets (TH1, TH2, and TH17) and cytokine (IFN-γ, IL-4, and IL-17) secretion levels by flow cytometry and ELISA analysis, respectively.

RESULTS

Results demonstrated reduced pneumococcal IgG and TH1 cell levels due to NK cell depletion. Nevertheless, in contrast to these observations, IFN-γ secretion levels after in vitro PPV-23 treatment of splenocytes did not exhibit any statistically significant difference between the two mice groups.

CONCLUSIONS

The data indicate a positive contribution of NK cells to both T-cell and B-cell responses triggered against pneumococcal vaccination. Further studies are required to confirm our data and investigate the potential benefit of NK cell targeting in promoting vaccine efficacy, especially in the elderly population who continues to be affected significantly by pneumococcal pneumonia.

Estimation of baseline IgG antibody levels to 23 pneumococcal vaccine-type capsular polysaccharides in healthy vaccine naïve Indian adults

Since immunological responses to pneumococcal vaccines are assessed by a fold-increase in antibody levels relative to pre-immunization levels, it is therefore critical to determine baseline antibody levels to establish putative threshold as a measure of normal response. Herein, for the first time, we measured baseline IgG antibody levels in 108 healthy unvaccinated Indian adults using WHO-recommended ELISA. Median baseline IgG concentration ranged between 0.54 µg/mL to 12.35 µg/mL. Highest levels of baseline capsule polysaccharide (cPS)-specific IgG were found against types 14, 19A, and 33F. Whereas, lowest baseline IgG levels were observed against types 3, 4, and 5. Overall, ∼79 % of study population had median baseline IgG levels ≥1.3 µg/mL against 74 % of cPS's. Substantial baseline antibody levels in unvaccinated adults were observed. The study would be critical in bridging gaps in baseline immunogenicity data and may offer a valuable foundation for evaluating immune response of Indian adults to pneumococcal vaccination.

T cell phenotype in paediatric heart transplant recipients

Paediatric heart transplantation recipients suffer an increased incidence of infectious, autoimmune and allergic problems. The relative roles of thymus excision and immunosuppressive treatments in contributing to these sequelae are not clear. We compared the immunological phenotypes of 25 heart transplant recipients (Tx), 10 children who underwent thymus excision during non-transplantation cardiac surgery (TE) and 25 age range-matched controls, in two age bands: 1-9 and 10-16 years. Significant differences from controls were seen mainly in the younger age band with Tx showing lower CD3 and CD4 cell counts whilst TE showed lower CD8 cell counts. Naïve T cell and recent thymic emigrant proportions and counts were significantly lower than controls in both groups in the lower age band. T cell recombination excision circle (TREC) levels were lower than controls in both groups in both age bands. There were no differences in regulatory T cells, but in those undergoing thymus excision in infancy, their proportions were higher in TE than Tx, a possible direct effect of immunosuppression. T cell receptor V beta spectratyping showed fewer peaks in both groups than in controls (predominantly in the older age band). Thymus excision in infancy was associated with lower CD8 cell counts and higher proportions of Tregs in TE compared to Tx. These data are consistent with thymus excision, particularly in infancy, being the most important influence on immunological phenotype after heart transplantation.

Isolating polysaccharide IgG pneumococcal antibody responses by pre-adsorption of conjugate vaccine serotypes: A modified approach for the conjugate vaccine era

BACKGROUND

Assessment of pure polysaccharide response to the 23-valent pneumococcal polysaccharide vaccine (PPV23) can be biased by previous exposure to the conjugate vaccine (PCV). We applied pre-analytical modification to the existing ELISA by pre-incubating serum with PCV.

METHODS

PCV-adsorbed and non-adsorbed sera were prepared before measuring the concentration of anti-pneumococcal capsular polysaccharide (PCP) IgG antibodies by the whole pneumococcal ELISA. Paired pre and post-pneumococcal vaccination sera from 73 subjects were analyzed and the baseline anti-PCP IgG for each sample was subtracted from the post-vaccination value to measure vaccine responses. Absolute change in titers and fold changes were then compared between both methods.

RESULTS

In the PCV-vaccinated group (n = 28), pre-adsorption with PCV significantly reduced the vaccine responses compared to non-adsorbed sera [median increase in anti-PCP titers: 27.55 mg/l and 45.98 mg/l, respectively]. In addition, the median fold change dropped significantly from 3.026 to 2.313. In PPV23-vaccinated immunocompetent subjects (n = 28) there was a significant difference in anti-PCP responses with PCV adsorption [median values: 73.71 mg/l without and 51.04 mg/l with adsorption]. All the antibody deficiency patients (n = 17) displayed poor PPV23 responses. Although PPV23 responsiveness was not statistically different between both methods, we have observed a trend for lower anti-PCP IgG titers in PCV-adsorbed sera compared to non-adsorbed ones. Serotype-specific IgG analysis using a multiplexed bead-based immunoassay performed on 10 paired samples confirmed that the adsorption observed is specific to PCV serotypes.

CONCLUSION

Pre-analytical modification to the conventional ELISA by removing the PCV-specific serotypes may differentiate true polysaccharide response from recall response induced by previous PCV vaccination.

Clinical and immunological features in a cohort of patients with partial DiGeorge syndrome followed at a single center

DiGeorge syndrome (DGS) is a primary immunodeficiency characterized by various degrees of T-cell deficiency. In partial DGS (pDGS), other risk factors could predispose to recurrent infections, autoimmunity, and allergy. The aim of this study was to assess the effect of different factors in the development of infections, autoimmunity, and/or allergy in patients with pDGS. We studied 467 pDGS patients in follow-up at Great Ormond Street Hospital. Using a multivariate approach, we observed that palatal anomalies represent a risk factor for the development of recurrent otitis media with effusion. Gastroesophageal reflux/dysphagia and asthma/rhinitis represent a risk factor for the development of recurrent upper respiratory tract infections. Allergy and autoimmunity were associated with persistently low immunoglobulin M levels and lymphopenia, respectively. Patients with autoimmunity showed lower levels of CD3⁺, CD3⁺CD4⁺, and naïve CD4⁺CD45RA⁺CD27⁺ T lymphocytes compared with pDGS patients without autoimmunity. We also observed that the physiological age-related decline of the T-cell number was slower in pDGS patients compared with age-matched controls. The age-related recovery of the T-cell number depended on a homeostatic peripheral proliferation of T cells, as suggested by an accelerated decline of the naïve T lymphocytes in pDGS as well as a more skewed T-cell repertoire in older pDGS patients. These evidences suggest that premature CD4⁺ T-cell aging and lymphopenia induced spontaneous peripheral T-cell proliferation might contribute to the pathogenesis of autoimmunity in patients with pDGS. Infections in these patients represent, in most of the cases, a complication of anatomical or gastroenterological anomalies rather than a feature of the underlying immunodeficiency.

Prescribing Immunoglobulin Replacement Therapy for Patients with Non-classical and Secondary Antibody Deficiency: an Analysis of the Practice of Clinical Immunologists in the UK and Republic of Ireland

Background

Immunologists are increasingly being asked to assess patients with non-classical and secondary antibody deficiency to determine their potential need for immunoglobulin replacement therapy (IGRT). Immunoglobulin is a limited, expensive resource and no clear guidance exists for this broad patient group. The purpose of this survey is to establish what factors influence the decision to commence IGRT in adult patients, when diagnostic criteria for primary antibody deficiency are not fulfilled.

Methods

Under the auspices of the United Kingdom Primary Immunodeficiency Network (UKPIN), a study group was established which circulated an online questionnaire to the consultant body across the UK and Ireland. Results provided a snapshot of the current clinical practice of 71% of consultant immunologists, from 30 centers.

Results

In order of importance, factors which influence the decision to commence IGRT include number of hospital admissions with infection, serum IgG level, bronchiectasis, radiologically proven pneumonia, number of positive sputum cultures, number of antibiotic courses, and results of immunization studies. The commonest test vaccine used was Pneumovax 23 with measurement of serotype-specific responses at 4 weeks, with a threshold of 0.35 μg/ml in 2/3 of serotypes measured. Eighty-six percent of patients are treated with a trial of prophylactic antibiotics prior to consideration of IGRT. Efficacy of IGRT trial is assessed at between 6 and 12 months.

Conclusions

There was consistency in clinical practice using a combination of clinical history, evidence of infections, and vaccination testing for diagnosis. However, there was some variation in the implementation of this practice, particularly in vaccine choice and assessment of response to vaccination.

Immunological efficacy of pneumococcal vaccine strategies in HIV-infected adults: a randomized clinical trial

The aim of this study was to compare the immunologic response to a prime-boost immunization strategy combining the 13-valent conjugate pneumococcal vaccine (PCV13) with the 23-valent polysaccharide pneumococcal vaccine (PPSV23) versus the PPSV23 alone in HIV-infected adults. HIV-infected adults were randomized to receive PCV13 at week 0 followed by PPSV23 at week 4 (n = 31, prime-boost group) or PPSV23 alone at week 4 (n = 33, PPSV23-alone group). Serotype specific IgG geometric mean concentration (GMC) and functional oposonophagocytic (OPA) geometric mean titer (GMT) were compared for 12 pneumococcal serotypes shared by both vaccines at week 8 and week 28. The prime-boost vaccine group were more likely to achieve a ≥2-fold increase in IgG GMC and a GMC >1 ug/ml at week 8 (odds ratio (OR) 2.00, 95% confidence interval (CI) 1.46–2.74, p < 0.01) and week 28 (OR 1.95, 95% CI 1.40–2.70, p < 0.01). Similarly, the prime-boost vaccine group were more likely to achieve a ≥4-fold increase in GMT at week 8 (OR 1.71, 95% CI 1.22–2.39, p < 0.01) and week 28 (OR 1.6, 95% CI 1.15–2.3, p < 0.01). This study adds to evidence supporting current pneumococcal vaccination recommendations combining the conjugate and polysaccharide pneumococcal vaccines in the United States and Europe for HIV-infected individuals.

Recurrent invasive pneumococcal disease in children: underlying clinical conditions, and immunological and microbiological characteristics

Purpose

Clinical, immunological and microbiological characteristics of recurrent invasive pneumococcal disease (IPD) in children were evaluated, differentiating relapse from reinfection, in order to identify specific risk factors for both conditions.

Methods

All patients <18 years-old with recurrent IPD admitted to a tertiary-care pediatric center from January 2004 to December 2011 were evaluated. An episode of IPD was defined as the presence of clinical findings of infection together with isolation and/or pneumococcal DNA detection by Real-Time PCR in any sterile body fluid. Recurrent IPD was defined as 2 or more episodes in the same individual at least 1 month apart. Among recurrent IPD, we differentiated relapse (same pneumococcal isolate) from reinfection.

Results

593 patients were diagnosed with IPD and 10 patients died. Among survivors, 23 episodes of recurrent IPD were identified in 10 patients (1.7%). Meningitis was the most frequent form of recurrent IPD (10 episodes/4 children) followed by recurrent empyema (8 episodes/4 children). Three patients with recurrent empyema caused by the same pneumococcal clone ST306 were considered relapses and showed high bacterial load in their first episode. In contrast, all other episodes of recurrent IPD were considered reinfections. Overall, the rate of relapse of IPD was 0.5% and the rate of reinfection 1.2%. Five out of 7 patients with reinfection had an underlying risk factor: cerebrospinal fluid leak (n = 3), chemotherapy treatment (n = 1) and a homozygous mutation in MyD88 gene (n = 1). No predisposing risk factors were found in the remainder.

Conclusions

recurrent IPD in children is a rare condition associated with an identifiable risk factor in case of reinfection in almost 80% of cases. In contrast, recurrent IPD with pleuropneumonia is usually a relapse of infection.

Antibody and plasmablast response to 13-valent pneumococcal conjugate vaccine in chronic lymphocytic leukemia patients--preliminary report

BACKGROUND

Chronic lymphocytic leukemia (CLL) leads to significant immune system dysfunction. The predominant clinical presentation in 50% of patients involves recurrent, often severe, infections. Infections are also the most common (60-80%) cause of deaths in CLL patients. The scope of infections varies with the clinical stage of the disease. Treatment-naive patients typically present with respiratory tract infections caused by encapsulated bacteria Streptococcus pneumoniae and Haemophilus influenzae. Since 2012, the 13-valent pneumococcal conjugate vaccine (PCV13) has been recommended in the United States and some EU countries for pneumococcal infection prevention in patients with CLL (besides the long-standing standard, 23-valent pneumococcal polysaccharide vaccine, PPV23). The aim of this study was to compare the immune response to PCV13 in 24 previously untreated CLL patients and healthy subjects.

METHODS

Both groups were evaluated for: the levels of specific pneumococcal antibodies, the levels of IgG and IgG subclasses and selected peripheral blood lymphocyte subpopulations including the frequency of plasmablasts before and after immunization.

RESULTS

Adequate response to vaccination, defined as an at least two-fold increase in specific pneumococcal antibody titers versus pre-vaccination baseline titers, was found in 58.3% of CLL patients and 100% of healthy subjects. Both the CLL group and the control group demonstrated a statistically significant increase in the IgG2 subclass levels following vaccination (P = 0.0301). After vaccination, the frequency of plasmablasts was significantly lower (P<0.0001) in CLL patients in comparison to that in controls. Patients who responded to vaccination had lower clinical stage of CLL as well as higher total IgG, and IgG2 subclass levels. No significant vaccine-related side effects were observed.

CONCLUSIONS

PCV13 vaccination in CLL patients is safe and induces an effective immune response in a considerable proportion of patients. To achieve an optimal vaccination response, the administration of PCV13 is recommended as soon as possible following CLL diagnosis.

Re-examination of immune response and estimation of anti-Vi IgG protective threshold against typhoid fever-based on the efficacy trial of Vi conjugate in young children

BACKGROUND

The capsular polysaccharide of Salmonella enterica serovar Typhi, Vi antigen, is an essential virulence factor and a protective antigen. Similar to other polysaccharide vaccines, the protective action of Vi, both to the polysaccharide alone or when presented as a conjugate, is mediated by serum IgG Vi antibodies. The evaluation of Vi capsular polysaccharide based vaccines to prevent typhoid fever would be significantly facilitated by the identification of a "protective level" of serum antibodies to Vi antigen.

METHODS

The protective level of anti-Vi IgG against typhoid fever was derived from the protective efficacy and immune response of a Vi-rEPA conjugate vaccine efficacy trial. The estimation was derived by two methods: correlation of the percent efficacy and the antibody distribution profile in the vaccine group at a given period of observation, and use of the relative ratio of anti-Vi IgG levels between the vaccine and placebo groups greater or equal to the Relative Risk of typhoid fever used in the efficacy determination.

RESULTS

Both methods predicted a similar range of a minimum protective level of anti-Vi IgG between 1.4 and 2.0μg/ml (short term threshold). When applying a protective threshold of 10μg/ml at 6 months post immunization, an IgG level in excess of 1.4μg/ml was achieved by 90% of children at 46 months post immunization, consistent with an 89% level of protection over the duration of the study. We thus suggest that the proportion of children with Vi IgG>10μg/ml (long term threshold) 6 months after immunization may reflect the proportion protected over at least a 4 year period.

CONCLUSION

The current assignment of an anti-Vi IgG protective level may be of value when evaluating vaccine performance of future Vi conjugate vaccines.

Impact of analytical variability on clinical interpretation of multiplex pneumococcal serology assays

The response to pneumococcal vaccination can be used to assess a patient's humoral immune response to polysaccharide antigens. Multiplex assays measuring serotype-specific levels of pneumococcal antibodies are often used for this purpose, and clinical algorithms have been published to assist in the definition of an adequate immune response. We evaluated whether interlaboratory variability in multiplex pneumococcal serology assays would affect the clinical classification of the immune response. Specimens from 57 patients were analyzed at three reference laboratories with different multiplex assays to measure pneumococcal serology. Analytical correlation and clinical agreement in the classification of a patient's vaccination status by the three methods were compared. Although substantial variation in the quantitative antibody levels measured by different laboratories was seen, the qualitative classification of individual serologic results showed a high degree of agreement between labs and the ultimate classification of a patient as "protected" or "nonprotected" was the same for most patients. The majority of discordant classifications were driven by a systematic bias in results from one of the assays rather than by random error. These data suggest that the use of integrated assessments based on multiple serotypes can compensate for much of the analytical variability seen between laboratories. Knowledge of the analytical performance characteristics of a particular assay is most important when evaluating patients with results near clinical cut points.

Reference ranges and cutoff levels of pneumococcal antibody global serum assays (IgG and IgG2) and specific antibodies in healthy children and adults

Pneumococcal antibodies represent the acquisition of natural immunity. Determination of pneumococcal antibodies is an important screening tool for immunodeficiencies. Our study generated reference ranges and cutoff levels for pneumococcal antibody global serum assays correlated to a specific pneumococcal antibody ELISA. Specific pneumococcal antibody levels were measured from 457 children undergoing elective surgery and 46 healthy adult volunteers (88 with previous pneumococcal immunization from both groups), 22 severe immunodeficient subjects with ataxia telangiectasia (A-T, negative controls), and age-matched 36 healthy allergic asthmatics. We determined a representative panel of serotype-specific pneumococcal antibodies (serotype 4, 5, 6B, 7F, 14, 18C, 19F, 23F) by ELISA and global pneumococcal IgG and IgG2 antibodies by EIA. In vaccine-naïve healthy subjects, initial pneumococcal IgG geometric mean concentrations of 13.1 μg/ml were low in the first year of life and increased over the time, reaching adult levels (70.5 μg/ml) at age 8-12 years. In parallel, IgG2 antibodies increased from 20.7 % (0.5-1 year old) to adult proportions (>30 %) in preschoolers. Correlation between the pneumococcal IgG screening assay and specific pneumococcal antibody levels was acceptable (Pearson's coefficient r = 0.4455; p = 0.001). Cutoff levels showed high sensitivity, whereas specificity was high to moderate calculated from correlations with the specific ELISA. We provide reference ranges and cutoff levels for the interpretation of specific antibody determinations in the clinical setting. The global pneumococcal IgG/IgG2 assay is a suitable screening tool and correlates with the ELISA serotype-specific pneumococcal antibodies. However, results below our cutoff values should be re-evaluated by serotype-specific ELISA testing.

Measurement of antibodies to pneumococcal, meningococcal and haemophilus polysaccharides, and tetanus and diphtheria toxoids using a 19-plexed assay

The measurement of antibody responses to vaccination is useful in the assessment of immune status in suspected immune deficiency. Previous reliance on enzyme-linked immunoabsorbent assays (ELISA) has been cumbersome, time-consuming and expensive. The availability of flow cytometry systems has led to the development of multiplexed assays enabling simultaneous measurement of antibodies to several antigens. We optimized a flow cytometric bead-based assay to measure IgG and IgM concentrations in serum to 19 antigens contained in groups of bacterial subunit vaccines: pneumococcal vaccines, meningococcal vaccines, Haemophilus influenzae b (Hib), and tetanus and diphtheria toxoid vaccines. 89-SF was employed as the standard serum. The assay was used to determine specific antibody levels in serum from 193 healthy adult donors. IgG and pneumococcal IgM antibody concentrations were measurable across 3 log10 ranges encompassing the threshold protective IgG antibody levels for each antigen. There was little interference between antibody measurements by the 19-plexed assay compared with monoplexed assays, and a lack of cross-reactive IgG antibody, but evidence for cross-reacting IgM antibody for 3/19 pneumococcal antigens. 90th centile values for 15/19 IgG concentrations and 12/12 IgM concentrations of the 193 adult sera were within these ranges and percentages of sera containing protective IgG antibody levels varied from 4% to 95% depending on antigen. This multiplexed assay can simultaneously measure antibody levels to 19 bacterial vaccine antigens. It is suitable for use in standard clinical practice to assess the in vivo immune response to test vaccinations and measure absolute antibody levels to these antigens.

Active Immunization with Pneumolysin versus 23-Valent Polysaccharide Vaccine for Streptococcus pneumoniae Keratitis

PURPOSE

The purpose of this study was to determine whether active immunization against pneumolysin (PLY), or polysaccharide capsule, protects against the corneal damage associated with Streptococcus pneumoniae keratitis.

METHODS

New Zealand White rabbits were actively immunized with Freund's adjuvant mixed with pneumolysin toxoid (ψPLY), Pneumovax 23 (PPSV23; Merck, Whitehouse Station, NJ), or phosphate-buffered saline (PBS), before corneal infection with 10⁵ colony-forming units (CFU) of S. pneumoniae. Serotype-specific rabbit polyclonal antisera or mock antisera were passively administered to rabbits before either intravenous infection with 10¹¹ CFU S. pneumoniae or corneal infection with 10⁵ CFU of S. pneumoniae.

RESULTS

After active immunization, clinical scores of corneas of the rabbits immunized with ψPLY and Freund's adjuvant were significantly lower than scores of the rabbits that were mock immunized with PBS and Freund's adjuvant or with PPSV23 and Freund's adjuvant at 48 hours after infection (P ≤ 0.0010), whereas rabbits immunized with PPSV23 and Freund's adjuvant failed to show differences in clinical scores compared with those in mock-immunized rabbits (P = 1.00) at 24 and 48 hours after infection. Antisera from rabbits actively immunized with PPSV23 and Freund's adjuvant were nonopsonizing. Bacterial loads recovered from infected corneas were higher for the ψPLY- and PPSV23-immunized rabbits after infection with WU2, when compared with the mock-immunized rabbits (P ≤ 0.007). Conversely, after infection with K1443, the ψPLY-immunized rabbits had lower bacterial loads than the control rabbits (P = 0.0008). Quantitation of IgG, IgA, and IgM in the sera of ψPLY-immunized rabbits showed high concentrations of PLY-specific IgG. Furthermore, anti-PLY IgG purified from ψPLY-immunized rabbits neutralized the cytolytic effects of PLY on human corneal epithelial cells. Passive administration of serotype-specific antisera capable of opsonizing and killing S. pneumoniae protected against pneumococcal bacteremia (P ≤ 0.05), but not against keratitis (P ≥ 0.476).

CONCLUSIONS

Active immunization with pneumococcal capsular polysaccharide and Freund's adjuvant fails to produce opsonizing antibodies, and passive administration of serotype specific opsonizing antibodies offers no protection against pneumococcal keratitis in the rabbit, whereas active immunization with the conserved protein virulence factor PLY and Freund's adjuvant is able to reduce corneal inflammation associated with pneumococcal keratitis, but has variable effects on bacterial loads in the cornea.

Failure of antibody response to polysaccharide antigen in treated panhypopituitary adults

Although pituitary hormones are known to affect immune function, treated hypopituitarism is not a recognized cause of immune deficiency in humans. We set out to assess integrity of baseline and stimulated immune function in severely hypopituitary adults. Twenty-one panhypopituitary adults (group 1), on stable pituitary replacement including growth hormone, and 12 healthy volunteers (group 2) were studied. Lymphocyte subsets, pneumococcal antibody levels pre- and 1 month after polysaccharide vaccination, T cell numbers and in-vitro interferon (IFN)-gamma response were studied. There were no significant differences in T cell numbers or IFN-gamma secretion. B cell numbers were lower in group 1, especially those with low prolactin levels. Independent of this finding, nine of 21 patients in this group had low antibody response to polysaccharide antigen. This was most striking in those with low insulin-like growth factor 1 levels and appeared to be independent of the use of anti-convulsants or corticosteroid replacement. Significant humoral immune deficiency is seen in panhypopituitarism and may contribute to morbidity.

Clinical immunology review series: an approach to the use of the immunology laboratory in the diagnosis of clinical allergy

In the last 10 years UK immunology laboratories have seen a dramatic increase in the number and range of allergy tests performed. The reasons for this have been an increase in the incidence of immunoglobulin E (IgE)-mediated allergic disease set against a background of greater public awareness and more referrals for assessment. Laboratory testing forms an integral part of a comprehensive allergy service and physicians treating patients with allergic disease need to have an up-to-date knowledge of the range of tests available, their performance parameters and interpretation as well as the accreditation status of the laboratory to which tests are being sent. The aim of this review is to describe the role of the immunology laboratory in the assessment of patients with IgE-mediated allergic disease and provide an up-to-date summary of the tests currently available, their sensitivity, specificity, interpretation and areas of future development.

Anti-pneumococcal antibody titre measurement: what useful information does it yield?

Measuring and interpretation of the immune response to pneumococcal polysaccharides is a complex field, owing to the diversity of the pneumococcal polysaccharide capsular types, different vaccine formulations including both polysaccharide and conjugate vaccines, diverse pneumococcal serological assays, lack of immunogenicity data for the conjugate in a number of at-risk groups and complex vaccine schedules. Even the reasons for performing pneumococcal serology can be complex, as assays may be performed for one of two reasons: either to assess an individual's immune status to the pneumococcus or to discriminate between normal and abnormal humoral immunity. This review details a history of the pneumococcal serological assays and provides some insight into when serology can prove useful, including vaccination data for certain at-risk groups.

Dependence of correlations between antibody titres and opsonophagocytosis on pneumococcal serotype and patient morbidity in pre- and post-pneumococcal vaccination states

Pre- vs. post-vaccination changes in correlations between IgG concentrations (ELISA titres) and opsonophagocytic activity (OPA) against Streptococcus pneumoniae serotypes 6B, 14 and 23F induced by the 23-valent polysaccharide vaccine were studied in paired serum samples received from elderly individuals, haemodialysed patients and kidney transplant recipients by the Spanish Pneumococcal Reference Laboratory. The pre- and post-vaccination parameters considered were: ELISA and OPA titres and the percentage of subjects with post-vaccination OPA values above the cut-off levels; the correlations between OPA and ELISA (Spearman correlation coefficient, r); and the amount of IgG needed to obtain OPA (beta coefficient). Non-significant pre-vaccination correlations between OPA and ELISA were found. Vaccination increased the correlation coefficient between OPA and ELISA to a statistically significant level for serotypes 6B, 14 and 23F in samples from haemodialysed patients, for serotypes 14 and 23F in samples from elderly individuals, and for none of the serotypes in samples from transplant recipients. In all cases, except for serotype 23 in transplant recipients, vaccination increased the beta coefficient, indicating that lower amounts of IgG were needed to obtain high OPA titres. A globally lower response was obtained for serotype 23 and/or transplant recipients.

Laboratory Diagnosis of Specific Antibody Deficiency to Pneumococcal Capsular Polysaccharide Antigens

Background: Measurement of postimmunization antibody response to pneumococcal capsular polysaccharide (caps-PS) is the standard method to identify deficiency of antipolysaccharide antibody production. However, no standardized criteria have been defined for classification of patients into responders or nonresponders to caps-PS.

Methods: We vaccinated 37 healthy children and 39 healthy adults with Pneumovax® and measured the anti–caps-PS antibody response to 5 serotypes. We also measured antipneumococcal antibody titers in 82 patients with increased susceptibility to airway infection. The ELISA was performed according to the 3rd-generation assay format.

Results: The lower 5th percentile (cutoff) concentrations for the postimmunization antibody titer in healthy individuals were 0.67 mg/L, 0.45 mg/L, 0.46 mg/L, 0.31 mg/L, and 1.04 mg/L for serotypes 3, 4, 9N, 18C, and 19F, respectively. In 96% of healthy individuals, antibody responses higher than the cutoff concentration were seen for at least 3 of the 5 serotypes. Nine of 82 patients (11%) failed to mount an adequate antibody response for at least 4 of the 5 serotypes tested, whereas only 1 control (1.3%) failed to do so.

Conclusion: The cutoffs for antibody responses to caps-PS identified in this study appear useful for identifying individuals with an inadequate response to vaccine.

Memory switched B cell percentage and not serum immunoglobulin concentration is associated with clinical complications in children and adults with specific antibody deficiency and common variable immunodeficiency

Although idiopathic humoral immunodeficiencies are arbitrarily classified into specific antibody deficiency (SAD) or common variable immunodeficiency (CVID), this distinction does not accurately predict the risk of the bronchiectasis, one of the major long-term clinical complications in these patients. In this study, clinical complications were compared with laboratory markers of cellular and humoral immunity in fifty-five consecutive patients (27 children and 28 adults) attending regional immunology clinics in Manchester, United Kingdom. Reduced CD19(+)CD27(+)IgD(-) B cell percentage but not serum immunoglobulin levels or classification of patients into SAD and CVID was associated with a significantly higher prevalence of bronchiectasis (OR 0.4 (0.2-0.8), P = 0.001), splenomegaly (OR 0.2 (0.1-0.5), P = 0.001) and autoimmunity (OR 0.4 (0.2-0.7), P = 0.003). We conclude that in patients with idiopathic humoral immunodeficiencies assessment of B cell switching more accurately predicts clinical prognosis than either classification of patients into SAD and CVID or serum immunoglobulin concentrations.

Circulating levels of B lymphocyte stimulator in patients with rheumatoid arthritis following rituximab treatment: relationships with B cell depletion, circulating antibodies, and clinical relapse

OBJECTIVE

To assess the effects of B lymphocyte depletion on serum B lymphocyte stimulator (BLyS; trademark of Human Genome Sciences, Rockville, MD) levels in patients with rheumatoid arthritis (RA), and to assess the relationship of serum BLyS levels with peripheral blood B cell depletion, levels of autoantibodies and antimicrobial antibodies, the return of peripheral blood B cells, and clinical relapse.

METHODS

Fifteen patients with active RA underwent rituximab-based B cell depletion therapy (BCDT). Disease activity was assessed clinically, peripheral blood CD19+ B cell counts were determined by flow cytometry, and serum levels of BLyS, IgM, IgA, and IgG rheumatoid factors (RFs), anti-cyclic citrullinated peptide, and antimicrobial antibodies were assessed using enzyme-linked immunosorbent assays.

RESULTS

Peripheral blood B cell depletion was achieved in all 15 patients, and an American College of Rheumatology 20% response was achieved in 13 patients. Following clinical relapse, 7 patients underwent at least 1 additional cycle of BCDT. In every case, serum BLyS levels markedly rose post-BCDT and remained elevated for at least 1-2 months. Serum levels of RF, but not those of anti-tetanus toxoid or anti-pneumococcal polysaccharide antibodies, fell significantly. A decline in serum BLyS levels was associated with the reemergence of B cells in peripheral blood, which, in turn, antedated clinical relapse by variable periods of time. The patterns of B cell depletion, serum BLyS and antibody levels, and clinical relapse for each BCDT cycle were remarkably similar in re-treated patients.

CONCLUSION

Rituximab-based BCDT leads to marked increases in serum BLyS levels. This may contribute significantly to the survival and/or regeneration of B cell populations capable of triggering clinical relapse.

B cell depletion therapy in systemic lupus erythematosus: Effect on autoantibody and antimicrobial antibody profiles

OBJECTIVE

Autoantibody production in patients with systemic lupus erythematosus (SLE) is associated with abnormalities of B cell function and phenotype. Clinical responses to B cell depletion therapy (BCDT), based on rituximab, are encouraging. Therefore, we undertook this study to investigate the effect of BCDT on antibody profiles.

METHODS

Serial sera from 16 patients with active, refractory SLE were assayed for antinucleosome antibodies, anti-double-stranded DNA (anti-dsDNA), anti-extractable nuclear antigen, anti-tetanus toxoid, and antibodies to pneumococcal capsular polysaccharide for at least 1 year following BCDT. Anti-dsDNA antibodies derived from the V(H)4.34 immunoglobulin germ line gene (9G4+) were also measured.

RESULTS

All patients achieved peripheral B cell depletion and improved clinically for at least 3 months. Antinucleosome and anti-dsDNA antibodies decreased to a mean +/- SD of 64 +/- 37% and 38 +/- 33% of baseline values, respectively, by 6-8 months post-BCDT. Levels of other autoantibodies and antimicrobial antibodies were generally unchanged. In the 9 of 16 patients who were still well at 1 year, anti-dsDNA antibodies fell to 42 +/- 36% of baseline values at 6-8 months and to 37 +/- 33% at 10-14 months. In patients who had disease flares within 1 year of BCDT, levels of these antibodies decreased to 60 +/- 40% and 83 +/- 93% of baseline values at 6-8 months and at 10-14 months, respectively. Circulating anti-dsDNA antibodies were positive for 9G4 expression in 4 of 6 patients tested, and flares in 2 of these patients were accompanied by rises in 9G4+ anti-dsDNA antibodies.

CONCLUSION

These observations suggest that B cell clones committed to producing antinucleosome and anti-dsDNA antibodies, including the V(H)4.34 subpopulation of anti-dsDNA antibodies, have a relatively rapid turnover compared with B cell clones producing other antibodies. There was also a trend toward a greater and more sustained decrease in anti-dsDNA antibodies in patients with clinical benefit lasting >1 year.

Influence of methotrexate, TNF blockers and prednisolone on antibody responses to pneumococcal polysaccharide vaccine in patients with rheumatoid arthritis

OBJECTIVE

To compare antibody responses to 23-valent pneumococcal vaccine (Pneumovax) in controls and patients with established rheumatoid arthritis (RA) treated with TNF blockers, methotrexate (MTX) or a combination of both.

METHODS

Patients with RA (n = 149) and healthy controls (n = 47) were vaccinated. Treatment with TNF blockers (etanercept or infliximab) and MTX was given to 50 patients, and 62 patients were treated with TNF blockers alone or with other DMARDs. MTX alone was given to 37 patients. Concentrations of immunoglobulin G (IgG) antibodies against pneumococcal capsular polysaccharides 23F and 6B were measured by enzyme-linked immunoassay before and 4-6 weeks after vaccination. An immune response was defined as a twofold or higher increase in antibody concentration following vaccination.

RESULTS

Prevaccination antibody levels for both 23F and 6B were similar in the patient groups. Antibody concentrations after vaccination increased significantly in all groups. Patients treated with TNF blockers without MTX showed better immune responses than those treated with TNF blockers in combination with MTX (P = 0.037 for 23F and P = 0.004 for 6B) or MTX alone (P<0.001 for both 23F and 6B). RA patients given MTX alone had the lowest immune responses. Prednisolone treatment did not influence the responses.

CONCLUSIONS

Patients treated with TNF blockers and controls showed similar responses to vaccination. In contrast, patients treated with MTX had reduced responses regardless of anti-TNF treatment. The findings do not argue against the use of pneumococcal vaccination in RA patients undergoing treatment with TNF blockers.

Functional and molecular evaluation of lymphocytes

The laboratory plays a central role in the evaluation of immune function and is critical in the diagnosis and treatment of immune deficiencies. The range of options available to evaluate lymphocyte function has expanded dramatically as our understanding of the immune system has expanded. As the choices of laboratory tests increase, so also does the need to choose testing in such a way as to appropriately direct the evaluation. Typically, this approach involves starting with screening tests and, on the basis of the results of these tests, deciding whether more sophisticated and expensive testing is warranted. The remarkable developments over the past decade leading to the identification of numerous gene defects underlying a variety of immune deficiencies has moved mutation analysis into the realm of the clinical laboratory. This information could be indispensable for immune deficiency diagnosis, prenatal screening, carrier detection, and family counseling. In this review a sequential approach to evaluating lymphocyte function is presented, starting with readily available screening tests and followed by more complex in vitro testing, including the application of newer assays. The various approaches are presented from the perspective of appropriate use and information garnered, whereas actual details of test procedures are not discussed but are referenced. The evolution of immune function testing suggests that it will continue to develop, and future assays are likely to provide even more insight into specific aspects of the immune response and be linked to immune deficiencies not yet defined.