Selective IgM Deficiency: Clinical and Laboratory Features of 17 Patients and a Review of the Literature

Refractory and Recurrent Skin Manifestations in an Adult With Selective Immunoglobulin M Deficiency

Selective immunoglobulin M (IgM) deficiency (sIgMD) is a rare immunodeficiency disorder characterized by decreased serum levels of IgM. Symptoms of sIgMD include repeated infections and allergic manifestations such as asthma and allergic rhinitis. The etiology and pathology of sIgMD remain largely unknown. Moreover, no genetic cause of sIgMD and associated symptoms has been established. Herein, we describe a 47-year-old female with sIgMD who presented with repeated fevers of unknown cause since childhood. She was referred to our department because of recently developed severe dermatitis without a history of atopic dermatitis or asthma. In addition to histological evaluation by skin biopsy, immunological parameters were investigated in her peripheral blood, and the cellular immunity profile was determined by flow cytometry. The patient with refractory skin manifestations was found to have sIgMD with normal surface levels of IgM in the B cells. Along with recurrence and exacerbation in dermatitis, she showed an increase in peripheral blood eosinophils and serum IgE levels, suggesting an underlying allergic mechanism. The present case strongly indicates the importance of measuring serum IgM levels when seeing patients with recurring fever and intractable skin manifestations.

Selective IgM Deficiency: Evidence, Controversies, and Gaps

Selective Immunoglobulin M deficiency (SIgMD) has been recently included in the inborn errors of immunity (IEI) classification by the International Union of Immunological Societies Expert Committee. The understanding of SIgMD is still extremely limited, especially so in cases of SIgMD in the pediatric population. The epidemiology of SIgMD in the pediatric population is still unknown. The pathogenesis of SIgMD remains elusive, and thus far no genetic nor molecular basis has been clearly established as a definitive cause of this primary immunodeficiency. Recurrent respiratory infections represent the main clinical manifestations in children, followed by allergic and autoimmune diseases. No conclusive data on the correct therapeutic management of SIgMD are available. Although, for most SIgMD patients, Ig replacement therapy is not required, it may be recommended for patients with significantly associated antibody deficiency and recurrent or severe infections. Prophylactic antibiotics and the prompt treatment of febrile illness are crucial. There is insufficient evidence on the prognosis of this condition. Therefore, further studies are required to define the disease trajectories and to increase our understanding of the molecular mechanisms underlying SIgMD in order to facilitate a better clinical, immunological, and prognostic characterization of the condition and develop tailored therapeutic management strategies.

Clinical and immunological phenotypes of selective IgM deficiency in children: Results from a multicenter study

BACKGROUND

A few studies assessed the clinical and immunological features of selective IgM deficiency (SIgMD), especially in the pediatric age. We aimed to characterize the clinical and immunological phenotypes of a cohort of pediatric patients with SIgMD according to the different diagnostic criteria available.

METHODS

In this multicenter study, we evaluated pediatric SIgMD patients diagnosed at the Pediatric Clinic in Pavia, Italy, or through the Italian Primary Immunodeficiency NETwork (IPINET) and monitored changes in their diagnosis over a time frame that ranges from several months to several years.

RESULTS

Forty-eight patients with SIgMD were included (mean serum IgM: 33 mg/dL). The most common clinical manifestations were recurrent infections (67%) and allergies (48%). Subgroup analysis according to SIgMD definition criteria of the European Society for Immunodeficiencies (ESID) showed no significant difference in clinical manifestations, also considering the group with additional immunological abnormalities. Sixteen patients had long-term follow-up, during which 87% preserved their SIgMD diagnosis, while two patients showed a reduction in IgA in addition to low IgM.

CONCLUSIONS

Our data suggest that the identification of a reduction in serum IgM in children should lead to a complete immunological work-up to obtain a comprehensive clinical and immunological characterization of the patient. The follow-up of these patients is fundamental to define the disease evolution and appropriate management.

Skin Manifestations in Patients with Selective Immunoglobulin E Deficiency

Selective immunoglobulin E deficiency (SIgED) is still an unrecognised primary immunodeficiency despite several observations supporting its existence. This study aimed to describe the skin manifestations associated with SIgED. We retrospectively assessed medical records of patients with SIgED, the diagnosis being based on serum IgE levels ≤2 Uk/L associated with normal serum levels of immunoglobulins G, M, and A. A total of 25 patients (24 female) with SIgED were included in the study. Eleven patients (44%) presented chronic spontaneous urticaria (CSU), five (20%) angioedema always associated with CSU, five erythema (20%), and six eczema (24%). Other, less frequent manifestations were lichen planus, anaphylactoid purpura, thrombocytopenic purpura, bullous pemphigoid, bullous pyoderma gangrenosum, and atypical skin lymphoproliferative infiltrate associated with reactive lymphadenopathy, chronic cholestasis, arthritis, and fibrosing mediastinitis. Fifteen patients (60%) had different types of associated autoimmune diseases, Hashimoto's thyroiditis being the most frequent (n = 5, 20%), followed by arthritis (n = 4, 16%), autoimmune hepatitis, neutropenia, vitiligo, and Sjögren's syndrome (n = 2, 8% each). Five malignancies were diagnosed in four patients (16%). An ultralow IgE serum level may be the only biomarker that reveals the presence of a dysregulated immune system in patients with a broad spectrum of skin manifestations.

Treatment with IgM-enriched intravenous immunoglobulins (IgM-IVIg) enhances clearance of stroke-associated bacterial lung infection

Post-stroke infection is a common complication of stroke that is associated with poor outcome. We previously reported that stroke induces an ablation of multiple sub-populations of B cells and reduces levels of IgM antibody, which coincides with the development of spontaneous bacterial pneumonia. The loss of IgM after stroke could be an important determinant of infection susceptibility and highlights this pathway as a target for intervention. We treated mice with a replacement dose of IgM-enriched intravenous immunoglobulin (IgM-IVIg) prior to and 24 h after middle cerebral artery occlusion (MCAO) and allowed them to recover for 2 d or 5 d post-surgery. Treatment with IgM-IVIg enhanced bacterial clearance from the lung after MCAO and improved lung pathology but did not impact brain infarct volume. IgM-IVIg treatment induced immunomodulatory effects systemically, including rescue of splenic plasma B cell numbers and endogenous mouse IgM and IgA circulating immunoglobulin concentrations that were reduced by MCAO. Treatment attenuated MCAO-induced elevation of selected pro-inflammatory cytokines in the lung. IgM-IVIg treatment did not increase the number of lung mononuclear phagocytes or directly modulate macrophage phagocytic capacity but enhanced phagocytosis of Staphylococcus aureus bioparticles in vitro. Low dose IgM-IVIg contributes to increased clearance of spontaneous lung bacteria after MCAO likely via increasing availability of antibody in the lung to enhance opsonophagocytic activity. Immunomodulatory effects of IgM-IVIg treatment may also contribute to reduced levels of damage in the lung after MCAO. IgM-IVIg shows promise as an antibacterial and immunomodulatory agent to use in the treatment of post-stroke infection.

Evaluation of the health status outcome among inpatients treated for Amphetamine Addiction

Amphetamine is one of the most abuser drugs in Saudi Arabia. The aim of this study was to evaluate health status outcome at baseline and after detoxification in amphetamine users through the evaluation of the body mass index, renal function tests, cardiac biomarkers, gonadal hormonal levels, and oxidative stress markers. A cross-sectional study was conducted on 90 participants. Sixty participants were hospitalized patients for treatment of addiction and 30 participants were healthy volunteers. This study was performed at a psychiatric and rehabilitation center, in Qassim region, in the Kingdom of Saudi Arabia. Participants were divided into: group I = control; group II = amphetamine users and group III = amphetamine plus cannabis users. Socio-demographic data was collected. The urinary amphetamine level, Severity Dependence Scale (SDS), body mass index (BMI), vital signs; serum levels of troponin T (TnT), immunoglobulin M (IgM), immunoglobulin G (IgG), luteinizing Hormone (LH), testosterone Hormone (TSTS), urea, creatinine, malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) were measured on admission and after detoxification. The results showed that the BMI was significantly decreased while, vital signs such as heart rate, blood pressure and respiratory rate were significantly increased in all abusers and returned to normal values after the detoxification period. The cardiac biomarker troponin T was significantly increased and reversed after detoxification. The immune system was evaluated through assessing serum levels of immunoglobulin (Ig) M and IgG. The immune system remained immunocompromised in drug users, and IgM and IgG levels did not reach the level of control group after treatment. Luteinizing and testosterone hormones were evaluated. Both hormones were increased on admission and improved after the detoxification period. Renal function showed no significant differences between drug users and the control group. In the evaluation of the antioxidant system, there was a significant increase in serum MDA, SOD, GPx, and CAT levels compared to healthy controls. After the detoxification phase, these oxidative stress biomarkers still remained elevated. The current results have shown the addiction of amphetamine and cannabis exert detrimental effects on different body organs and the exert major consequences on the health status of drug users. The present study showed that, there was no improvement in the levels of oxidative stress biomarkers, although an improvement was observed in the other parameters after the detoxification phase.

Spectrum of Disease Manifestations in Patients with Selective Immunoglobulin E Deficiency

BACKGROUND

Selective IgE deficiency (SIgED) has been previously evaluated in selected patients from allergy units. This study investigates the effects of SIgED on the entire population in a hospital setting and sought to delineate in detail the clinical aspects of SIgED.

METHODS

A retrospective study of the data obtained from electronic medical records of 52 adult patients (56% female) with a mean age of 43 years and IgE levels of <2.0 kU/L with normal immunoglobulin (Ig) IgG, IgA, and IgM levels, seen at our hospital, without selection bias, from 2010 to 2019.

RESULTS

Recurrent upper respiratory infections were recorded in 18 (34.6%) patients, pneumonia was recorded in 16 (30.7%) patients, bronchiectasis was recorded in 16 (30.7%) patients, and asthma was recorded in 10 (19.2%) patients. Eighteen patients (34.6%) suffered autoimmune clinical manifestations either isolated (19%) or combining two or more diseases (15%), Hashimoto's thyroiditis being the most frequent (19%), which was followed by arthritis (10%) and thrombocytopenia and/or neutropenia (5.7%). Other less frequent associations were Graves' disease, primary sclerosing cholangitis, Sjögren's syndrome, and autoimmune hepatitis. Eczematous dermatitis (15.3%), chronic spontaneous urticaria (17.3%), and symptoms of enteropathy (21%) were also highly prevalent. Thirty percent of patients developed malignancies, with non-Hodgkin lymphomas (13.4%) being the most prevalent.

CONCLUSIONS

The clinical manifestations of SIgED encompass a variety of infectious, non-infectious complications, and malignancy. Since it cannot be ruled out that some type of selection bias occurred in the routine assessment of IgE serum Ievels, prospective studies are required to better characterize SIgED and to determine whether it should be added to the list of antibody deficiencies.

Selective IgM deficiency: Follow-up and outcome

BACKGROUND

Selective IgM deficiency (sIgMD) is classified under primary immunodeficiencies (PID). This study aimed to define the clinical and immunologic features of sIgMD.

PATIENT AND METHODS

We assessed a retrospective medical record of patients who fulfilled the diagnostic criteria for sIgMD in a pediatric immunology department.

RESULTS

There were 55 patients with sIgMD. Out of 55 patients, 13 (23.6%) patients, diagnosed with a well-defined PID disease, and nine, evaluated as transient hypogammaglobulinemia, were excluded in the follow-up. The ratio of the sIgMD was %0.12 in the outpatient clinic of pediatric immunology (33/27,000). Out of 33 patients, eight (24,2%) were asymptomatic during the follow-up period. Fifteen (45.4%) patients presented with upper/lower respiratory and skin infections. Six patients (18%) had chromosomal anomaly, or syndrome (trisomy 21, 22q11.2 deletion 1p deletion, CHARGE syndrome, and Cohen syndrome). Six (18%) had autoimmune/inflammatory diseases, such as Behcet's disease, immune thrombocytopenic purpura, Crohn's disease, Guillain-Barre syndrome, and diabetes mellitus. Five (15%) had allergic disorders. Three patients (9%) developed malignancy. The PID diagnoses were combined immunodeficiency, common variable immunodeficiency, chronic granulomatous disease, adenosine deaminase deficiency, and congenital neutropenia.

CONCLUSION

Genetic disorders, autoimmune/inflammatory, and allergic diseases may accompany sIgMD. Approximately 25% of the patients were asymptomatic in our series. Patients had increased malignancy risk. We diagnosed about 25% of the patients having low IgM with a specific PID in the follow-up period. Thus, patients with sIgMD should be followed up regularly in immunology clinics.

Treatment and management of primary antibody deficiency: German interdisciplinary evidence-based consensus guideline

This evidence-based clinical guideline provides consensus-recommendations for the treatment and care of patients with primary antibody deficiencies (PADs). The guideline group comprised 20 clinical and scientific expert associations of the German, Swiss, and Austrian healthcare system and representatives of patients. Recommendations were based on results of a systematic literature search, data extraction, and evaluation of methodology and study quality in combination with the clinical expertise of the respective representatives. Consensus-based recommendations were determined via nominal group technique. PADs are the largest clinically relevant group of primary immunodeficiencies. Most patients with PADs present with increased susceptibility to infections, however immune dysregulation, autoimmunity, and cancer affect a significant number of patients and may precede infections. This guideline therefore covers interdisciplinary clinical and therapeutic aspects of infectious (e.g., antibiotic prophylaxis, management of bronchiectasis) and non-infectious manifestations (e.g., management of granulomatous disease, immune cytopenia). PADs are grouped into disease entities with definitive, probable, possible, or unlikely benefit of IgG-replacement therapy. Summary and consensus-recommendations are provided for treatment indication, dosing, routes of administration, and adverse events of IgG-replacement therapy. Special aspects of concomitant impaired T-cell function are highlighted as well as clinical data on selected monogenetic inborn errors of immunity formerly classified into PADs (APDS, CTLA-4-, and LRBA-deficiency).

Neurolisteriosis in a previously asymptomatic patient with serum IgM deficiency: a case report

BACKGROUND

Listeria monocytogenes is an opportunistic pathogen of the central nervous system commonly associated with impaired cell-mediated immunity. We hereby present a case of adult neurolisteriosis where the only immunological feature persistently present was serum IgM deficiency, suggesting that non-specific humoral immunity may also play a central role in the control of neuroinvasion by Listeria monocytogenes.

CASE PRESENTATION

A 62-year-old male who had never experienced severe infections presented with headache, nuchal rigidity and confusion. Neuroimaging was normal and lumbar puncture revealed pleiocytosis (760 leukocytes/mm3) and hypoglycorrhachia (34 mg/dL). The patient was treated empirically for bacterial meningitis. Indeed, further analysis of the CSF showed infection by Listeria monocytogenes, which was accompanied by reduced serum IgM levels that persisted well beyond the period of acute bacterial infection. Levels of IgG and IgA isotypes, along with peripheral blood counts of major leukocyte subsets, were at the same time largely preserved. Intriguingly, the absence of membrane-bound IgM on B cells was essentially complete in the acute post-infection period leading to a remarkable recovery after 12 months, suggesting that mechanisms other than defective membrane expression are underlying serum deficiency.

CONCLUSIONS

As far as we know, this is the first reported case of neurolisteriosis associated with IgM deficiency in an adult individual without a history of severe infections or other underlying conditions. A possible role of circulating IgM against invasive disease caused by Listeria monocytogenes, particularly in the early course of host-pathogen interaction, is discussed.

The epidemiology and clinical features of selective immunoglobulin M deficiency: A single-center study in China

Background

Selective immunoglobulin M deficiency (SIgMD) is a rare primary immunodeficiency that is frequently reported in Western countries. However, large epidemiological and clinical studies of SIgMD in China are still lacking. Herein, we describe a cohort of SIgMD subjects in a large tertiary university hospital in China.

Methods

A cross‐sectional study included 139 668 participants at First Affiliated Hospital of Wenzhou Medical University from January 2014 to October 2018 was conducted. Individuals with a serum IgM level less than 0.3 g/L with normal levels of serum IgA and IgG were defined as having SIgMD.

Result

A total of 63 subjects met the criteria for SIgMD(63/139668, 0.045%), with a male‐to‐female ratio of 0.85, aged from 19 to 99 years. The most common clinical manifestation was autoimmune disorders (38/63, 60.32%), while the second most common manifestation was infections (21/63, 33.33%). Neither allergies nor tumors were found among these 63 SIgMD subjects. Most importantly, there were 30 patients with systemic lupus erythematosus among these 63 SIgMD subjects, accounting for 47.62% of all SIgMD subjects.

Conclusion

To our knowledge, we describe here the first large single‐center cohort of adult patients affected by SIgMD in China. The most common clinical manifestation was autoimmune disorders, specifically systemic lupus erythematosus.

The antibody/microbiota interface in health and disease

The human intestine is densely colonized with commensal microbes that stimulate the immune system. While secretory Immunoglobulin (Ig) A is known to play a crucial role in gut microbiota compartmentalization, secretory IgM, and systemic IgG have recently been highlighted in host-microbiota interactions as well. In this review, we discuss important aspects of secretory IgA biology, but rather than focusing on mechanistic aspects of IgA impact on microbiota, we stress the current knowledge of systemic antibody responses to whole gut microbiota, in particular their generation, specificities, and function. We also provide a comprehensive picture of secretory IgM biology. Finally, therapeutic and diagnostic implications of these novel findings for the treatment of various diseases are outlined.

Post-Craniopharyngioma and Cranial Nerve-VI Palsy Update on a MS Patient with Major Depression and Concurrent Neuroimmune Conditions

We report the case of a male multiple sclerosis (MS) patient with type 2 diabetes (T2D), asthma, major depression (MD or major depressive disorder, MDD), and other chronic conditions, after his recent difficulties with craniopharyngioma and cranial nerve-VI (CN6) palsy. In addition, we show magnetic resonance image and spectroscopy (MRI, MRS), Humphrey's Visual Field (HVF), and retinal nerve fiber layer thickness (RNFLT) findings to explain the changes in the patient's health, and discuss the methods that helped/help him sustain productivity and euthymia despite long-standing problems and new CNS changes.

Acute-onset Autoimmune Hepatitis in a Patient with Selective Immunoglobulin M Deficiency

Selective immunoglobulin M deficiency (SIGMD) is an uncommon primary immunodeficiency disorder. We herein report an SIGMD patient with autoimmune hepatitis. A 21-year-old Japanese man was transferred to our hospital because of acute liver dysfunction. His serum IgM level was low, whereas those of IgG and IgA were normal, indicating that he had SIGMD. We diagnosed him with acute-onset autoimmune hepatitis, and his liver function test findings gradually recovered with corticosteroid administration. Although SIGMD with autoimmune diseases has been reported, the clinical features and pathogenesis have not yet been clarified. We have summarized previous reports on SIGMD patients with autoimmune diseases.

Plasma therapy leads to an increase in functional IgA and IgM concentration in the blood and saliva of a patient with X-linked agammaglobulinemia

BACKGROUND

Patients with X-linked agammaglobulinemia (XLA) are protected against invasive bacterial infections due to IgG replacement therapy, but are still at higher risk for mucosal infections of the gut and respiratory tract. This might be explained by to the lack of IgA and IgM, as these antibodies are especially important for protection against invading bacterial pathogens on the mucosal surface.

METHODS

In an attempt to eliminate a chronic norovirus infection in a patient with X-linked agammaglobulinemia, fresh frozen plasma (FFP) was given two times a week for 3 weeks. At each visit, pre- and post-FFP infusion serum and saliva was collected to determine IgG-, IgA- and IgM-concentrations and serum half-life was calculated. Functionality of the immunoglobulins pre- and post-FFP infusion in both serum and saliva was tested by measuring complement activation, agglutination and killing of non-typeable Haemophilus influenzae (NTHi).

RESULTS

Administration of FFP failed to eradicate the chronic norovirus infection. Serum IgA and IgM half-life was 4.2 ± 0.3 and 3.8 ± 0.3 days, respectively. The presence of serum IgM was associated with increased complement binding and complement-mediated killing of NTHi. IgA in saliva was detectable post-FFP and was associated with increased agglutination of NTHi. IgM in saliva was not detectable.

CONCLUSIONS

We conclude that FFP treatment, although ineffective in clearing a chronic norovirus infection in this single patient, might be beneficial to prevent or eliminate bacterial infections in XLA patients by increasing IgM dependent complement-mediated killing in serum and IgA dependent bacterial agglutination on the mucosal surface.

Challenges in investigating patients with isolated decreased serum IgM: The SIMcal study

The clinical consequences of isolated decreased serum immunoglobulin (Ig)M are not sufficiently known. Therefore, it is difficult to determine the clinical policy following such a finding. Only few reported IgM‐deficient patients fulfil the European Society for Immunodeficiencies (ESID) diagnostic criteria for selective IgM deficiency (true sIgMdef), or their diagnosis is uncertain due to insufficient laboratory data (possible sIgMdef). Decreased serum IgM is often incidentally found in asymptomatic adults. The objective of our study was to further characterize true sIgMdef and to compare the European data collected through the ESID Registry community (tertiary centres) to our previously published Dutch cohort (secondary centre). Fifteen centres (12 countries) participated with 98 patients. Patients were excluded if serum IgM was only determined once (n = 14), had normalized (n = 8), or if they also had other immunological abnormalities (n = 15). Ten patients (5 adults) completely fulfilled the ESID criteria for true sIgMdef. Age‐matched cut‐off values varied widely between centres; when using the ESID diagnostic protocol reference values, only six patients (five adults) had true sIgMdef. Because of these small numbers, further analyses were performed in patients with true or possible sIgMdef (13 adults, 48 children). Respiratory infections were commonly reported at presentation (adults 54%, children 60%). Symptomatic adults had lower serum IgM levels (mean 0.27 g/L, 95% CI 0.22‐0.31) than those without symptoms (mean 0.33 g/L, 95% CI 0.30‐0.36; P = 0.02). To be able to explore the clinical consequences of true sIgMdef, we should fully analyse and accurately describe those patients in whom a decreased serum IgM is found.

Autoimmunity and immunodeficiency at the crossroad: autoimmune disorders as the presenting feature of selective IgM deficiency

Selective immunoglobulin M deficiency (sIgMD) is an immunodeficiency with undefined pathogenesis and commonly presenting with recurrent infections. ¹ The European Society for Immunodeficiencies Registry defines sIgMD as a serum IgM level repeatedly below 2 SD of normal with normal levels of serum IgA, IgG and IgG subclasses, normal vaccination responses, absence of T-cell defects and absence of causative external factors. Rarely it can also be associated with autoimmune diseases. ^2-7 Here we describe a patient with primary sIgMD; who presented with multiple autoimmune diseases without a history of recurrent infections and we provide a short literature review on sIgMD and autoimmune diseases.

Hypomorphic Mutations in the BCR Signalosome Lead to Selective Immunoglobulin M Deficiency and Impaired B-cell Homeostasis

B cell activation via the B cell receptor (BCR) signalosome involves participation of signaling molecules such as BTK and BLNK. Genetic defects in these molecules are known to impair B cell differentiation and subsequently lead to agammaglobulinemia. Here we identified novel mutations in BTK and BLNK in two unrelated patients that perturb the intrinsic B-cell receptor signaling pathway and lead to selective IgM deficiency, whereas production of other immunoglobulin isotypes and IgG antibody response remain intact. Currently it is unknown how BCR signaling strength affects mature B cell development in humans. Both patients show reduced levels of BCR signalosome phosphorylation as well as impaired BCR-dependent Ca²⁺ influx, which was accompanied by a marked decrease in IgD⁺IgM⁺CD27⁺ MZ-like B-cells. We further describe reduced expression of essential B cell differentiation factors such as BAFF-R and T-Bet in the patients' B-cells, which might contribute to the observed deficiency of MZ-like B cells. MZ-like B cells are known to produce natural IgM antibodies that play an essential role in immune homeostasis. By using surface plasmon resonance (SPR) technology and a synthetic blood group A trisaccharide as antigen we were able to show that both patients lack the presence of anti-blood group A IgM considered to be prototypical natural antibodies whereas IgG levels were normal. Antibody binding dynamics and binding affinity of anti-blood group A IgG were comparable between patients and healthy controls. These results indicate that human IgM deficiency can be associated with signaling defects in the BCR signalosome, defective production of natural IgM antibodies in the blood group A/B/0 system and abnormalities in B cell development.

Limited Innovations After More Than 65 Years of Immunoglobulin Replacement Therapy: Potential of IgA- and IgM-Enriched Formulations to Prevent Bacterial Respiratory Tract Infections

Patients with primary immunoglobulin deficiency have lower immunoglobulin levels or decreased immunoglobulin function, which makes these patients more susceptible to bacterial infection. Most prevalent are the selective IgA deficiencies (~1:3,000), followed by common variable immune deficiency (~1:25,000). Agammaglobulinemia is less common (~1:400,000) and is characterized by very low or no immunoglobulin production resulting in a more severe disease phenotype. Therapy for patients with agammaglobulinemia mainly relies on prophylactic antibiotics and the use of IgG replacement therapy, which successfully reduces the frequency of invasive bacterial infections. Currently used immunoglobulin preparations contain only IgG. As a result, concurrent IgA and IgM deficiency persist in a large proportion of agammaglobulinemia patients. Especially patients with IgM deficiency remain at risk for recurrent infections at mucosal surfaces, which includes the respiratory tract. IgA and IgM have multiple functions in the protection against bacterial infections at the mucosal surface. Because of their multimeric structure, both IgA and IgM are able to agglutinate bacteria efficiently. Agglutination allows for entrapment of bacteria in mucus that increases clearance from the respiratory tract. IgA is also important for blocking bacterial adhesion by interfering with bacterial adhesion receptors. IgM in its place is very well capable of activating complement, therefore, it is thought to be important in complement-mediated protection at the mucosal surface. The purpose of this Mini Review is to highlight the latest advances regarding IgA- and IgM-enriched immunoglobulin replacement therapy. We describe the different IgA- and IgM-enriched IgG formulations, their possible modes of action and potential to protect against respiratory tract infections in patients with primary immunoglobulin deficiencies.

Chronic Pulmonary Histoplasmosis Identified in a Young Patient with Selective Immunoglobulin M Deficiency

Chronic histoplasmosis is typically diagnosed in patients who are immunocompromised or severely debilitated and who either live in or who have travelled to endemic areas. We report the case of a young, otherwise immunocompetent male patient who presented to a New York hospital with lobar consolidation and was found to have chronic pulmonary histoplasmosis. He described no history of travel to an endemic area. Immunological workup later revealed selective immunoglobulin M (IgM) deficiency. The literature has suggested a link between IgM deficiency and fungal infections. Recent research has also proposed a link between autoimmunity and IgM deficiency. Our clinical vignette describes the case of a patient with selective IgM deficiency who was diagnosed with pulmonary histoplasmosis without any clinical evidence of autoimmune disease.

IgM Augments Complement Bactericidal Activity with Serum from a Patient with a Novel CD79a Mutation

Antibody replacement therapy for patients with antibody deficiencies contains only IgG. As a result, concurrent IgM and IgA deficiency present in a large proportion of antibody deficient patients persists. Especially patients with IgM deficiency remain at risk for recurrent infections of the gastrointestinal and respiratory tract. The lack of IgM in the current IgG replacement therapy is likely to contribute to the persistence of these mucosal infections because this antibody class is especially important for complement activation on the mucosal surface. We evaluated whether supplementation with IgM increased serum bactericidal capacity in vitro. Serum was collected from a patient with agammaglobulinemia and supplemented with purified serum IgM to normal levels. Antibody and complement deposition on the bacterial surface was determined by multi-color flow cytometry. Bacterial survival in serum was determined by colony-forming unit counts. We present a patient previously diagnosed with agammaglobulinemia due to CD79A (Igα) deficiency revealing a novel pathogenic insertion variant in the CD79a gene (NM_001783.3:c.353_354insT). Despite IgG replacement therapy and antibiotic prophylaxis, this patient developed a Campylobacter jejuni spondylodiscitis of lumbar vertebrae L4–L5. We found that serum IgM significantly contributes to complement activation on the bacterial surface of C. jejuni. Furthermore, supplementation of serum IgM augmented serum bactericidal activity significantly. In conclusion, supplementation of intravenous IgG replacement therapy with IgM may potentially offer greater protection against bacterial infections, also in the context of increasing antibiotic resistance.