Immunoglobulin deficiencies and impaired immune response to polysaccharide antigens in adult patients with recurrent community-acquired pneumonia

Vagus nerve stimulation modulates distinct acetylcholine receptors on B cells and limits the germinal center response

Acetylcholine is produced in the spleen in response to vagus nerve activation; however, the effects on antibody production have been largely unexplored. Here, we use a chronic vagus nerve stimulation (VNS) mouse model to study the effect of VNS on T-dependent B cell responses. We observed lower titers of high-affinity IgG and fewer antigen-specific germinal center (GC) B cells. GC B cells from chronic VNS mice exhibited altered mRNA and protein expression suggesting increased apoptosis and impaired plasma cell differentiation. Follicular dendritic cell (FDC) cluster dispersal and altered gene expression suggested poor function. The absence of acetylcholine-producing CD4+ T cells diminished these alterations. In vitro studies revealed that α7 and α9 nicotinic acetylcholine receptors (nAChRs) directly regulated B cell production of TNF, a cytokine crucial to FDC clustering. α4 nAChR inhibited coligation of CD19 to the B cell receptor, presumably decreasing B cell survival. Thus, VNS-induced GC impairment can be attributed to distinct effects of nAChRs on B cells.

High Frequency of Specific Polysaccharide Antibody Deficiency in Adults With Unexplained, Recurrent and/or Severe Infections With Encapsulated Bacteria

BACKGROUND

Primary immunodeficiencies (PIDs) in adults are mainly revealed by recurrent and/or severe bacterial infections. The objective of this study was to evaluate a systematic research strategy of PIDs in adults with unexplained bacterial infections, with a special focus on specific polysaccharide antibody deficiency (SPAD).

METHODS

In this prospective multicenter study, inclusion criteria were recurrent benign upper and lower respiratory tract infections (RTIs) for at least two years (group 1), at least one upper or lower RTI requiring hospitalization (group 2), and/or at least one invasive infection documented with encapsulated bacteria (group 3). Main exclusion criteria were all local and general conditions that could explain infections. If no PID diagnosis was made, response to polysaccharide antigens was assessed using a pneumococcal polysaccharide vaccine.

RESULTS

From March 2015 to March 2020, 118 patients were included (37 males, median age of 41 years): 73, 17, and 28 in groups 1, 2, and 3, respectively. Forty-seven PIDs were diagnosed, giving an estimated frequency of 39.8% (95% confidence interval [CI] [30.4, 48.8]). SPAD was the most frequent diagnosis by far (n = 37/47, 78.7%), and was made in 23, 5, and 9 patients from groups 1 to 3, respectively. All SPAD patients received conjugate vaccines and, according to their infectious history, were on surveillance or treated with preventive antibiotics (n = 6) and/or with immunoglobulins replacement therapy (n = 10), the latter being dramatically efficient in all cases.

CONCLUSIONS

Considering its high prevalence among adults with unexplained recurrent and/or severe bacterial infections, SPAD should be screened in those patients.

CLINICAL TRIALS REGISTRATION

NCT02972281.

Diagnostic Vaccination in Clinical Practice

Testing the antibody response to vaccination (diagnostic vaccination) is crucial in the clinical evaluation of primary immunodeficiency diseases. Guidelines from the American Academy of Allergy, Asthma & Immunology (AAAAI) provide detailed recommendations for diagnostic vaccination with pure pneumococcal polysaccharide vaccines (PPV). However, the degree of compliance with these guidelines and the utility of the guidelines in actual practice are undescribed. To address this, we systematically evaluated diagnostic vaccination in adult patients with suspected primary immunodeficiency diseases in a single tertiary center from 2011 to 2016 (n = 229). We found that full compliance with the AAAAI guidelines was achieved for only 39 patients (17%), suggesting that the guidelines are not easy to follow. Worse, interpretation according to the guidelines was heavily influenced by which serotype-specific antibodies that were used for the evaluation. We found that the arbitrary choices of serotype-specific antibodies could change the fraction of patients deemed to have ‘adequate immunity’ by a factor of four, exposing an inherent flaw in the guidelines. The flaw relates to dichotomous principles for data interpretation under the AAAAI guidelines. We therefore propose a revised protocol for diagnostic vaccination limited to PPV vaccination, subsequent antibody measurements, and data interpretation using Z-scores. The Z-score compiles multiple individual antibody levels, adjusted for different weighting, into one single continuous variable for each patient. In contrast to interpretation according to the AAAAI guidelines, the Z-scores were robust to variations in the choice of serotype-specific antibodies used for interpretation. Moreover, Z-scores revealed reduced immunity after vaccination in the patients with recurrent pneumonia (a typical symptom of antibody deficiency) compared with control patients. Assessment according to the AAAAI guidelines failed to detect this difference. We conclude that our simplified protocol and interpretation with Z-scores provides more robust clinical results and may enhance the value of diagnostic vaccination.

Follicular dendritic cell dysfunction contributes to impaired antigen-specific humoral responses in sepsis-surviving mice

Sepsis survivors exhibit impaired responsiveness to antigen (Ag) challenge associated with increased mortality from infection. The contribution of follicular dendritic cells (FDCs) in the impaired humoral response in sepsis-surviving mice is investigated in this study. We demonstrated that mice subjected to sepsis from cecal ligation and puncture (CLP mice) have reduced NP-specific high-affinity class-switched Ig antibodies (Abs) compared with sham-operated control mice following immunization with the T cell-dependent Ag, NP-CGG. NP-specific germinal center (GC) B cells in CLP mice exhibited reduced TNF-α and AID mRNA expression compared with sham-operated mice. CLP mice showed a reduction in FDC clusters, a reduced binding of immune complexes on FDCs, and reduced mRNA expression of CR2, ICAM-1, VCAM-1, FcγRIIB, TNFR1, IKK2, and LTβR compared with sham-operated mice. Adoptive transfer studies showed that there was no B cell-intrinsic defect. In summary, our data suggest that the reduced Ag-specific Ab response in CLP mice is secondary to a disruption in FDC and GC B cell function.

Pneumonia

Pneumonia is a common acute respiratory infection that affects the alveoli and distal airways; it is a major health problem and associated with high morbidity and short-term and long-term mortality in all age groups worldwide. Pneumonia is broadly divided into community-acquired pneumonia or hospital-acquired pneumonia. A large variety of microorganisms can cause pneumonia, including bacteria, respiratory viruses and fungi, and there are great geographical variations in their prevalence. Pneumonia occurs more commonly in susceptible individuals, including children of <5 years of age and older adults with prior chronic conditions. Development of the disease largely depends on the host immune response, with pathogen characteristics having a less prominent role. Individuals with pneumonia often present with respiratory and systemic symptoms, and diagnosis is based on both clinical presentation and radiological findings. It is crucial to identify the causative pathogens, as delayed and inadequate antimicrobial therapy can lead to poor outcomes. New antibiotic and non-antibiotic therapies, in addition to rapid and accurate diagnostic tests that can detect pathogens and antibiotic resistance will improve the management of pneumonia.

Diagnosis and management of Specific Antibody Deficiency

Specific antibody deficiency is a primary immunodeficiency disease recognized by the International Union of Immunology Societies and defined by recurrent respiratory infections with normal immunoglobulins, but diminished antibody responses to polysaccharide antigens after vaccination with the 23 valent pneumococcal polysaccharide vaccine. Clinical immunologists struggle with diagnosis and treatment, because the definition of an adequate response to immunization remains controversial. Specific antibody deficiency is managed clinically with close follow-up and prompt treatment of infections, antibiotic prophylaxis, or immune globulin therapy. Treatment is individualized using clinical judgment and existing practice guidelines, which will likely evolve as more studies become available.

IGA Antibody Induced by Immunization With Pneumococcal Polysaccharides Is a Prognostic Tool in Common Variable Immune Deficiencies

The evaluation of the response to vaccination in patients with inborn errors of immunity is a tool to evaluate T-dependent and T-independent antibody residual function of B lymphocytes and it is part of the diagnostic definition for Common Variable Immune Deficiencies. Currently used classifications for Common Variable Immune Deficiencies patients are based on the frequency of B cell subsets, and have been proven as a valid instrument for identification of patients at higher risk of infectious and non-infectious complications. This 6-years period observational study delineated the measurement of specific IgA antibodies induced by a 23-valent pneumococcal polysaccharides vaccine by a standardized ELISA for the quantification of IgA antibodies to all 23 pneumococcal serotypes as an additional prognostic marker in 74 CVID patients. The inability to mount an IgA-mediated response against the pneumococcal polysaccharide antigens or the inability to maintain the antibody response over time identified poor IgA CVID responders with severe immunological impairment, great risk of co-morbidities, and poor prognosis. The division of CVID patient into specific IgA-non responders and IgA-responders discriminated better than other CVID classifications for infectious risk, while it overlapped for non-infectious complications. Our study suggested to add the evaluation of the antibody response by the 23-valent IgA assay in the clinical monitoring of CVID patients.

Low Baseline Pneumococcal Antibody Titers Predict Specific Antibody Deficiency, Increased Upper Respiratory Infections, and Allergy Sensitization

BACKGROUND

Inadequate titers of pneumococcal antibody (PA) are commonly present among patients with recurrent respiratory infections.

OBJECTIVE

We sought to determine the effect of the degree of inadequacy in baseline PA titers on the subsequent polysaccharide vaccine response, the incidence of sinusitis, and allergic conditions.

METHODS

A total of 313 patients aged 6 to 70 years with symptoms of recurrent respiratory infections were classified by baseline-pPA (percentage of protective [≥1.3 µg/mL] PA serotypes/total tested serotypes) and postvaccination pPA (post-pPA): Group A (adequate baseline-pPA), Group B (inadequate baseline-pPA, adequate post-pPA, responders), and Group C (inadequate baseline-pPA, inadequate postpPA, nonresponders, specific antibody deficiency [SAD]). Immunity against Streptococcus pneumoniae was defined as adequate when the pPA was ≥70%. Each group and combined groups, Group AB (inadequate baseline-pPA), and Group BC (adequate post-pPA) were analyzed for demographics, history of sinusitis, recurrent sinusitis in the following year, allergic conditions, and association with inadequate individual serotype titers.

RESULTS

Over 80% of patients with respiratory symptoms had inadequate baseline-pPA. Baseline-pPA and SAD prevalence are inversely related (odds ratio = 2.02, 95% CI: 1.15-3.57, P = .01). Inadequate serotype 3 antibody titer is highly associated with SAD (odds ratio = 2.02, 96% CI: 1.61-5.45, P < .01). The groups with inadequate pPA (Group B and C, or BC) had significantly higher percentage of patients with chronic rhinosinusitis (P < .001), allergic sensitization, and allergic rhinitis (P < .05). Group A contained higher percentage of patients with recurrent upper airway infections (P < .001).

CONCLUSION

Low baseline-pPA and low antibody titers to serotype 3 are highly associated with SAD, increased incidence of respiratory infections including CRS and allergic conditions.

Comparison of four adjuvants revealed the strongest protection against lethal pneumococcal challenge following immunization with PsaA-PspA fusion protein and AS02 as adjuvant

Streptococcuspneumoniae, or pneumococcus, is a major respiratory-tract pathogen that causes high levels of mortality and morbidity in infants and elderly individuals. Despite the development of various capsular polysaccharide vaccines to prevent pneumococcal disease, it remains epidemic. Pneumococcal surface protein A (PspA) is a highly immunogenic surface protein existing in all strains of S. pneumoniae, and it can elicit immunizing protection against pneumococcal infection. In our previous studies, a fusion protein (PsaA-PspA23), consisting of PspA and pneumococcal surface antigen A (PsaA), displayed greater immunogenicity and provided better protection in mice against S. pneumoniae strains than either PsaA or PspA. In this study, the fusion protein PsaA-PspA23, together with PspA4, was formulated with four adjuvants Al(OH)₃, MF59, AS03, and AS02, and subsequently subjected to dose optimization and immunological evaluation for determination of the antibody titers, bacterial burden, survival rates, and levels of cytokines in mice. All vaccines with high adjuvant doses displayed higher antigen-specific immunoglobulin G (IgG) titers. Bacterial burdens were notably decreased to different extents in the lungs and blood of mice immunized with the antigen and various adjuvants. Among these adjuvants, AS02 provided outstanding protection against challenge with pathogenic bacteria from different families and clades; it also induced high titers of IgG1 and IgG2a. Moreover, only AS02 elicited high levels of cytokines, such as TNF-α, IFN-γ, IL-2, and IL-4. These results suggest that PsaA-PspA23 and PspA4 formulated with AS02 may potentially be used as a subunit vaccine against deadly pneumococcal infection.

Serotypes With Low Invasive Potential Are Associated With an Impaired Antibody Response in Invasive Pneumococcal Disease

Pneumococcal polysaccharide vaccines may elicit a hyporesponse under certain conditions. There is limited knowledge, however, on the type of specific antibody response in individuals with invasive pneumococcal disease (IPD). The aim of this study was to investigate the functional antibody response in patients with IPD caused by different serotypes. Pre-immune and convalescent sera from 40 patients (age 14–91 years) with IPD caused by serotypes with low (serotype 3, 19F, and 23F) and high (1, 4, 7F, and 14) invasive potential were investigated. For each patient, the homologous serotype-specific antibody concentration was determined. The functionality of induced antibodies post-IPD was evaluated in an opsonophagocytic assay (OPA). Undetectable or decreased pneumococcal killing in OPA following IPD, i.e., a nonfunctional antibody response, was observed in 24 of 40 patients (60%). Patients with nonfunctional antibody responses had lower serotype specific IgG antibody ratios post-IPD than patients with increased OPA titres. A nonfunctional antibody response was associated with low invasive serotypes (3, 19F, and 23F, p = 0.015). In conclusion, a nonfunctional antibody response may follow IPD, and was in our cohort associated to serotypes with low invasive potential. These findings need to be confirmed in a larger material.

Low Levels of Immunoglobulins and Mannose-Binding Lectin Are Not Associated With Etiology, Severity, or Outcome in Community-Acquired Pneumonia

Background

Disease severity and outcome in community-acquired pneumonia (CAP) depend on the host and on the challenge of the causal microorganism(s). We measured levels of immunoglobulins (Igs) and complement in 257 hospitalized adults with CAP and examined the association of low levels of Igs or complement to microbial etiology, disease severity, and short-term and long-term outcome.

Methods

Serum Igs were analyzed in blood samples obtained at admission and at 6 weeks postdischarge if admission levels were low. Serum complement deficiencies were screened with a total complement activity enzyme-linked immunosorbent assay (ELISA), with further analyzes performed if justified. Disease severity was assessed by the CURB-65 severity score. Short-term outcome was defined as a composite end point of intensive care unit (ICU) admission and 30-day mortality, and long-term outcome as 5-year all-cause mortality.

Results

At admission, 87 (34%) patients had low levels of at least 1 Ig, with low IgG2 as the most prevalent finding (55/21%). IgG levels were lower in bacterial than viral CAP (8.48 vs 9.97 g/L, P = .023), but low Igs were not associated with microbial etiology. Fifty-five (21%) patients had low lectin pathway activity, of which 33 (13%) were mannose-binding lectin (MBL) deficient. Low admission levels of any Ig or MBL were not associated with disease severity, short-term outcome, or long-term outcome. Excluding patients defined as immunocompromised from analysis did not substantially affect these results.

Conclusion

In hospitalized adults with CAP, low admission levels of Igs or complement were in general not associated with microbial etiology, disease severity, short-term outcome, or long-term outcome.

Specific Antibody Deficiency: Controversies in Diagnosis and Management

Specific antibody deficiency (SAD) is a primary immunodeficiency disease characterized by normal immunoglobulins (Igs), IgA, IgM, total IgG, and IgG subclass levels, but with recurrent infection and diminished antibody responses to polysaccharide antigens following vaccination. There is a lack of consensus regarding the diagnosis and treatment of SAD, and its clinical significance is not well understood. Here, we discuss current evidence and challenges regarding the diagnosis and treatment of SAD. SAD is normally diagnosed by determining protective titers in response to the 23-valent pneumococcal polysaccharide vaccine. However, the definition of an adequate response to immunization remains controversial, including the magnitude of response and number of pneumococcal serotypes needed to determine a normal response. Confounding these issues, anti-polysaccharide antibody responses are age- and probably serotype dependent. Therapeutic strategies and options for patients with SAD are often based on clinical experience due to the lack of focused studies and absence of a robust case definition. The mainstay of therapy for patients with SAD is antibiotic prophylaxis. However, there is no consensus regarding the frequency and severity of infections warranting antibiotic prophylaxis and no standardized regimens and no studies of efficacy. Published expert guidelines and opinions have recommended IgG therapy, which are supported by observations from retrospective studies, although definitive data are lacking. In summary, there is currently a lack of evidence regarding the efficacy of therapeutic strategies for patients with SAD. We believe that it is best to approach each patient as an individual and progress through diagnostic and therapeutic interventions together with existing practice guidelines.

Assessment of disulfide and hinge modifications in monoclonal antibodies

During the last years there was a substantial increase in the use of antibodies and related proteins as therapeutics. The emphasis of the pharmaceutical industry is on IgG1, IgG2, and IgG4 antibodies, which are therefore in the focus of this article. In order to ensure appropriate quality control of such biopharmaceuticals, deep understanding of their chemical degradation pathways and the resulting impact on potency, pharmacokinetics, and safety is required. Criticality of modifications may be specific for individual antibodies and has to be assessed for each molecule. However, some modifications of conserved structure elements occur in all or at least most IgGs. In these cases, criticality assessment may be applicable to related molecules or molecule formats. The relatively low dissociation energy of disulfide bonds and the high flexibility of the hinge region frequently lead to modifications and cleavages. Therefore, the hinge region and disulfide bonds require specific consideration during quality assessment of mAbs. In this review, available literature knowledge on underlying chemical reaction pathways of modifications, analytical methods for quantification and criticality are discussed. The hinge region is prone to cleavage and is involved in pathways that lead to thioether bond formation, cysteine racemization, and iso‐Asp (Asp, aspartic acid) formation. Disulfide or sulfhydryl groups were found to be prone to reductive cleavage, trisulfide formation, cysteinylation, glutathionylation, disulfide bridging to further light chains, and disulfide scrambling. With regard to potency, disulfide cleavage, hinge cleavage, disulfide bridging to further light chains, and cysteinylation were found to influence antigen binding and fragment crystallizable (Fc) effector functionalities. Renal clearance of small fragments may be faster, whereas clearance of larger fragments appears to depend on their neonatal Fc receptor (FcRn) functionality, which in turn may be impeded by disulfide bond cleavage. Certain modifications such as disulfide induced aggregation and heterodimers from different antibodies are generally regarded critical with respect to safety. However, the detection of some modifications in endogenous antibodies isolated from human blood and the possibility of in vivo repair mechanisms may reduce some safety concerns.

Recurrent pneumonia: a review with focus on clinical epidemiology and modifiable risk factors in elderly patients

Community-acquired pneumonia (CAP) is one of the most common reasons for physician visits and hospitalizations in North America. Rates of CAP increase with age and CAP is associated with significant morbidity and mortality, especially in the elderly. Though there is much written about the epidemiology and risk factors of incident (first episode) pneumonia, much less is known about recurrent pneumonia. Rates of recurrent pneumonia within 3-5-years of an episode of CAP are 9-12% with a median time to recurrence of 123-317 days and mortality ranging from 4 to 10%. Age ≥65-years-old and impaired functional status are the only patient characteristics that are independently associated with increased risk of recurrence. In terms of modifiable risk factors, only the use of proton-pump inhibitors and systemic and inhaled corticosteroids have consistently been associated with increased risk of recurrent pneumonia, while angiotensin-converting enzyme (ACE) inhibitors may exert a protective effect. Many chronic medical conditions typically associated with increased incident pneumonia-such as chronic obstructive pulmonary disease (COPD), neurological disease (resulting in dysphagia or silent aspiration), and heart failure-were not associated with increased risk of recurrent pneumonia. However, those who are immune-suppressed (e.g., immunoglobulin deficiencies) may be at increased risk of recurrent pneumonia. In summary, among those who survive an episode of pneumonia, recurrence is not uncommon, particularly in the elderly. Following recovery from an episode of pneumonia, patients should be evaluated for risk factors that would predispose to a second episode including seeking evidence of immunosuppression in younger patients and medication optimization, particularly in the elderly.

Hepatitis B vaccination uptake and correlates of serologic response among HIV-infected and uninfected men who have sex with men (MSM) in Bangkok, Thailand

BACKGROUND

Vaccination against hepatitis B virus (HBV) is recommended for all HBV-susceptible men who have sex with men (MSM). There is limited information on correlates of immunity to HBV vaccination in this group. We present serologic response rates to hepatitis B vaccine and identify factors associated with impaired response among HIV-uninfected and HIV-infected Thai MSM.

METHODOLOGY

HBV-susceptible volunteers were offered hepatitis B vaccination at months zero, one, and six. We measured baseline (pre-vaccination) total serum IgG and IgG subclasses (all participants), baseline CD4 count, and plasma HIV-1 viral load (PVL) (HIV+ participants). HBV serologies were retested at 12 months. Serologic responses were compared between all groups in men receiving three vaccine doses.

RESULTS

511/651 HIV-negative and 64/84 HIV-positive participants completed the three-dose series. Response rates in HIV-uninfected and -infected participants were 90.1% vs. 50.0% (p<0.0001). Median pre-vaccination IgG was higher among non-responders than responders overall (1238.9.0 vs. 1057.0mg/dL, p=0.003) and among HIV-infected participants (1534.0 vs. 1244.5mg/dL, p=0.005), but not significantly among HIV-uninfected participants (1105.5 vs. 1054.3mg/dL, p=0.96). Pre-vaccination IgG1 and IgG3 levels were higher among HIV-positive than HIV-negative participants (median 866.0 vs. 520.3, and 105.8 vs. 83.1mg/dL, respectively, p<0.0001). Among HIV-infected participants, median CD4 count in non-responders was 378 cells/μL vs. 431 cells/μL in responders (p=0.20). Median PVL in non-responders was 64,800 copies/mL vs. 15500 copies/mL in responders (p=0.04). Participants with pre-vaccination plasma IgG >1550 mg/dL and PVL >10,000 copies/mL were almost always non-responsive (p<0.01).

CONCLUSIONS

HIV infection was associated with poor vaccine responses. High plasma viral load, elevated pre-vaccination total serum IgG and elevated pre-vaccination IgG1 are associated with poorer response to vaccination among HIV-infected MSM. In this group, the combination of high PVL and pre-vaccination total IgG is highly predictive of vaccine failure.

Impaired function of antibodies to pneumococcal surface protein A but not to capsular polysaccharide in Mexican American adults with type 2 diabetes mellitus

The goal of the study was to determine baseline protective titers of antibodies to Streptococcus pneumoniae surface protein A (PspA) and capsular polysaccharide in individuals with and individuals without type 2 diabetes mellitus. A total of 561 individuals (131 individuals with diabetes and 491 without) were screened for antibodies to PspA using a standard enzyme-linked immunosorbent assay (ELISA). A subset of participants with antibodies to PspA were retested using a WHO ELISA to determine titers of antibodies to capsular polysaccharide (CPS) (serotypes 4, 6B, 9V, 14, 18C, 19A, 19F, and 23F). Functional activity of antibodies was measured by assessing their ability to enhance complement (C3) deposition on pneumococci and promote killing of opsonized pneumococci. Titers of antibodies to protein antigens (PspA) were significantly lower in individuals with diabetes than controls without diabetes (P = 0.01), and antibodies showed a significantly reduced complement deposition ability (P = 0.02). Both antibody titers and complement deposition were negatively associated with hyperglycemia. Conversely, titers of antibodies to capsular polysaccharides were either comparable between the two groups or were significantly higher in individuals with diabetes, as was observed for CPS 14 (P = 0.05). The plasma specimens from individuals with diabetes also demonstrated a higher opsonophagocytic index against CPS serotype 14. Although we demonstrate comparable protective titers of antibodies to CPS in individuals with and individuals without diabetes, those with diabetes had lower PspA titers and poor opsonic activity strongly associated with hyperglycemia. These results suggest a link between diabetes and impairment of antibody response.

Immunoglobulin G subclass levels and antibody responses to the 2009 influenza A (H1N1) monovalent vaccine among human immunodeficiency virus (HIV)-infected and HIV-uninfected adults

Immunoglobulin (Ig)G levels are important for antibody vaccine responses and IgG subclass deficiencies have been associated with severe 2009 influenza A (H1N1) infections. Studies have demonstrated variations in immune responses to the H1N1 vaccine, but the aetiology of this is unknown. We determined the associations between pre-vaccination overall and influenza-specific IgG subclass levels and 2009 H1N1-specific antibody responses post-vaccination (robust versus poor at day 28) stratified by human immunodeficiency virus (HIV) status. Logistic regression models were utilized to evaluate whether pre-vaccination IgG subclass levels were associated with the antibody response generated post-vaccination. We evaluated 48 participants as part of a clinical study who were stratified by robust versus poor post-vaccination immune responses. Participants had a median age of 35 years; 92% were male and 44% were Caucasian. HIV-infected adults had a median CD4 count of 669 cells/mm(3) , and 79% were receiving highly active anti-retroviral therapy. HIV-infected participants were more likely to have IgG2 deficiency (<240 mg/dl) than HIV-uninfected individuals (62% versus 4%, P < 0·001). No association of pre-vaccination IgG subclass levels (total or influenza-specific) and the antibody response generated by HIN1 vaccination in either group was found. In summary, pre-vaccination IgG subclass levels did not correlate with the ability to develop robust antibody responses to the 2009 influenza A (H1N1) monovalent vaccine. IgG2 deficiencies were common among HIV-infected individuals but did not correlate with poor influenza vaccine responses. Further investigations into the aetiology of disparate vaccine responses are needed.

Comparison of immunoglobulin G subclass concentrations in severe community-acquired pneumonia and severe pandemic 2009 influenza A (H1N1) infection

We compared immunoglobulin G (IgG) subclasses in patients with severe noninfluenza community-acquired pneumonia (CAP) to those in patients with severe pandemic 2009 influenza (H1N1) virus infection. Low IgG1 and IgG2 levels occurred often in the CAP group; however, H1N1 patients had lower IgG1 and IgG2 levels (5.4 versus 3.3 g/liter [P = 0.008] and 2.5 versus 1.2 g/liter [P < 0.001], respectively). Low IgG2 levels may be specifically linked to severe H1N1; however, it is not clear whether this association is related to H1N1 or to other features of severity.

Characterization of specific antibody deficiency in adults with medically refractory chronic rhinosinusitis

BACKGROUND

Specific antibody deficiency may predispose patients to recurrent respiratory tract infections. There is limited literature assessing specific antibody deficiency in chronic rhinosinusitis (CRS). This study evaluated the role of specific antibody deficiency in patients with CRS who have failed medical therapy.

METHODS

We performed a retrospective chart review of patients with CRS who underwent functional endoscopic sinus surgery and had prior assessment for humoral immunodeficiency. Each patient's record was reviewed for serum quantitative immunoglobulin G (IgG) and IgA and anti-Streptococcus pneumoniae antibody titers measured at baseline and 6 weeks postvaccination with the 23-valent unconjugated pneumococcal vaccine. Clinical characteristics, including asthma, atopy, and nasal polyps, were recorded.

RESULTS

Of the 129 CRS patients who met inclusion criteria, 93 (72%) had low baseline antipneumococcal titers. Fifteen (11.6%) patients were diagnosed with specific antibody deficiency based on an inadequate response to the pneumococcal polysaccharide vaccine. The group of patients with specific antibody deficiency had significantly lower serum IgA levels when compared with those patients with normal preimmunization titers (138 ± 67.3 versus 330 ± 356; p < 0.05). Patients with specific antibody deficiency had a significantly lower number of preimmunization protective antipneumococcal titers when compared with vaccine responders (1.41 versus 2.72; p < 0.0005).

CONCLUSION

This retrospective study indicates that patients with medically refractory CRS may have a high prevalence of low preimmunization antipneumococcal titers and specific antibody deficiency. Furthermore, lower serum IgA levels identified in these specific antibody deficiency patients suggests that a prospective study to further characterize this relationship is warranted.

Aetiology of, and risk factors for, recurrent community-acquired pneumonia

Recurrent community-acquired pneumonia (CAP) requiring hospitalization is a matter of particular concern. However, current information on its prevalence, aetiology and risk factors is lacking. To address these issues, we performed an observational analysis of a prospective cohort of hospitalized adults with CAP. Recurrence was defined as two or more episodes of CAP 1 month apart within 3 years. Patients with severe immunosuppression or local predisposing factors were excluded. Of the 1556 patients, 146 (9.4%) had recurrent CAP. The most frequent causative organism was Streptococcus pneumoniae, both in patients with recurrent CAP and in those without recurrence. Haemophilus influenzae, other Gram-negative bacilli and aspiration pneumonia were more frequent among patients with recurrent CAP, whereas Legionella pneumophila was rarely identified in this group. Independent factors associated with recurrent CAP were greater age, lack of pneumococcal vaccination, chronic obstructive pulmonary disease (COPD) and corticosteroid therapy. In a sub-analysis of 389 episodes of pneumococcal pneumonia, the only independent risk factor for recurrence was lack of pneumococcal vaccination. Recurrence of CAP is not a rare clinical problem and it occurs mainly in the elderly, patients with COPD, and those receiving corticosteroids. Our study provides support for recommending pneumococcal vaccination for adults at risk of pneumonia, including those with a first episode of CAP.

Clinical characteristics and outcomes of primary immunodeficiencies in Thai children: an 18-year experience from a tertiary care center

Introduction

Early diagnosis and treatment are keys to improve survival of patients with primary immunodeficiency diseases (PID). The clinical characteristics of these patients in Thailand were not well defined.

Objective

This study aimed to determine the clinical characteristics and outcomes of patients with PID in Thailand.

Methods

Medical records of PID patients in the past 18 years were reviewed.

Results

Sixty-seven children were registered. Antibody deficiencies were the most common PID (52.2%), followed by combined T cell and B cell immunodeficiencies (25.4%), other well-defined immunodeficiency syndromes (11.9%), and phagocytic defects (10.4%). The most common presentations of antibody deficiencies, combined T cell and B cell immunodeficiencies, and phagocytic defects were infection in the upper respiratory tract (74.3%), gastrointestinal tract (82.4%), and skin (85.7%), respectively. The highest mortality rate (52.9%) was found in severe combined immunodeficiency.

Conclusion

These results provide clinical features of PID in Thailand. Knowing these features will lead to prompt diagnosis and appropriate management.

Prevention of pneumococcal infection in a patient with normal immunoglobulin levels but impaired polysaccharide antibody production

BACKGROUND

Patients with normal immunoglobulin levels may have an impaired response to immunization with pneumococcal vaccine and increased susceptibility to infection with encapsulated organisms. In children, but not adults, immunoglobulin replacement has been shown to be effective in reducing the infection rate.

OBJECTIVE

To reduce the incidence of infection in an adult with impaired response to pneumococcal vaccine but normal serum IgG levels.

METHODS

Intravenous IgG, 350 mg/kg, was given every 4 weeks.

RESULTS

The patient, who was hospitalized 3 times in 3 years with respiratory tract infections and who had documented infection with Streptococcus pneumoniae and Haemophilus influenzae, did not require antibiotic therapy for more than 15 months while undergoing intravenous immunoglobulin replacement therapy.

CONCLUSION

Adults with impaired response to vaccination with polyvalent pneumococcal vaccine and normal IgG levels may benefit from replacement therapy.

Primary immunodeficiencies associated with pneumococcal disease

PURPOSE OF REVIEW

Streptococcus pneumoniae may cause disease in patients with a variety of primary immunodeficiencies. However, no previous review has dealt with the issue of which primary immunodeficiencies predispose affected individuals to pneumococcal disease. We thus reviewed the medical literature on cases of S. pneumoniae infection in patients with primary immunodeficiency diseases, with a particular emphasis on invasive pneumococcal disease.

RECENT FINDINGS

Primary immunodeficiency diseases comprise over 100 conditions, each associated with a variety of infections. Patients at high risk for pneumococcal disease include most if not all B-cell defects (whether due to an intrinsic B-cell anomaly or an impaired T-cell help), deficiencies of early components of the classical pathway of complement and C3 deficiency, congenital asplenia, anhidrotic ectodermal dysplasia with immunodeficiency (caused by impaired NF-kappaB activation), and interleukin-1 receptor associated kinase-4 deficiency. Patients with other complement deficiencies (alternative and third pathway) and hyperimmunoglobulin E syndrome show a lower risk, whereas patients with other known primary immunodeficiencies, such as phagocytic disorders, do not appear to be particularly vulnerable to S. pneumoniae.

SUMMARY

Antibody- and complement-mediated opsonization, splenic macrophages and interleukin-1 receptor associated kinase-4- and nuclear factor kappaB-mediated immune responses are crucial for protective immunity to S. pneumoniae. This information is useful, not only in increasing our understanding of human immunity to S. pneumoniae, but also in the diagnostic investigation of patients with pneumococcal disease.

Human IgG2 can form covalent dimers

Unlike IgA and IgM, IgG has not yet been shown to form covalent polymers. However in the presence of specific Ag, murine IgG3 has been shown to polymerize through noncovalent interactions. In contrast to the noncovalent oligomers found with murine IgG3, we have detected covalent dimers in three different recombinant human IgG2 Abs produced in myeloma cells. Both IgG2,kappa and IgG2,lambda can form dimers. In addition, analysis of pooled human gamma globulin and several normal sera revealed the presence of IgG2 dimers. The IgG2 dimers are in contrast to the noncovalent IgG dimers found in pooled sera of multiple donors resulting from idiotype/anti-idiotype (Id/anti-Id) interactions. Cyanogen bromide cleavage analysis suggests that one or more Cys residues in the gamma 2 hinge are involved in dimer assembly. The potential role of IgG2 dimers in immunity against carbohydrate Ags is discussed.

12. Primary immunodeficiency diseases

Although primary immunodeficiency disorders are relatively rare, intensive investigation of these disorders has yielded a great wealth of understanding of basic immunologic mechanisms in host defense, inflammation, and autoimmunity. These advances have led to important developments for the treatment not only of the primary immunodeficiencies but also for patients with secondary immunocompromised states, autoimmune disorders, hypersensitivity, graft rejection, and graft versus host disease. Correction of a form of severe combined immunodeficiency represents the first true success of human gene therapy. This review introduces the major clinical manifestations of primary immunodeficiency disorders, along with descriptions of essential elements of the pathophysiology of those disorders that have been defined at the molecular level. Key concepts in treatment are also presented. It is critical for the practicing primary care provider and allergist to maintain an index of suspicion for immunodeficiency. Early diagnosis offers the best opportunity for reduced morbidity and survival and is critical for accurate genetic counseling.