Abstract
IgM deficiency has been reported in patients with many autoimmune diseases treated with Rituximab (RTX). It has not been studied, in detail, in autoimmune mucocutaneous blistering diseases (AIMBD). Our objectives were: (i) Examine the dynamics of IgM levels in patients with and without RTX. (ii) Influence of reduced serum IgM levels on clinical and laboratory parameters. (iii) Explore the possible molecular and cellular basis for reduced serum IgM levels. This retrospective study that was conducted in a single-center from 2000 to 2020. Serial IgM levels were studied in 348 patients with five AIMBD (pemphigus vulgaris, pemphigus foliaceus, bullous pemphigoid, mucous membrane pemphigoid, and ocular cicatricial pemphigoid) and found decreased in 55 patients treated with RTX, IVIG, and conventional immunosuppressive therapy (CIST). Hence the incidence of decreased serum IgM is low. The incidence of decreased IgM in patients treated with RTX was 19.6%, in patients treated with IVIG and CIST, it was 52.8% amongst the 55 patients. IgM levels in the post-RTX group were statistically significantly different from the IVIG group (p<0.018) and CIST group (p<0.001). There were no statistically significant differences between the groups in other clinical and laboratory measures. Decreased serum IgM did not affect depletion or repopulation of CD19+ B cells. Patients in the three groups achieved clinical and serological remission, in spite of decreased IgM levels. Decrease in IgM was isolated, since IgG and IgA were normal throughout the study period. Decreased IgM persisted at the same level, while the patients were in clinical remission, for several years. In spite of persistent decreased IgM levels, the patients did not develop infections, tumors, other autoimmune diseases, or warrant hospitalization. Studies on IgM deficiency in knockout mice provided valuable insights. There is no universally accepted mechanism that defines decreased IgM levels in AIMBD. The data is complex, multifactorial, sometimes contradictory, and not well understood. Nonetheless, data in this study provides novel information that enhances our understanding of the biology of IgM in health and disease.
Highlights
IgM is an important molecule for many reasons
We present data on patients with pemphigus vulgaris (PV), pemphigus foliaceus (PF), bullous pemphigoid (BP), mucous membrane pemphigoid (MMP), and ocular cicatricial pemphigoid (OCP), who had decreased levels of serum IgM, during their systemic therapy
We present the data on patients with PV, PF, BP, MMP, and OCP who were treated with RTX, intravenous immunoglobulin (IVIG), and conventional immunosuppressive therapy (CIST), and in whom the levels of IgM were followed for long periods of time
Summary
IgM is an important molecule for many reasons. It is the first immunoglobulin produced as a part of the adaptive immune system, which has evolved over 500 million years [1]. The varying and similar structures of the molecule are present in jawed fishes, amphibians, reptiles, birds, and mammals [2]. In all these species, it helps discriminate self and non-self, protect against pathogens, and provides the memory of previous infections [3]. In spite of its evolutionary and current importance in the immune system, it has not been studied in detail in autoimmune diseases IgM and IgD are regarded as ancient isotypes and play an important role in the emergence of the significant diversity of the immune response [4, 5].
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