Immunoglobulin M (IgM) is the largest antibody class that plays a leading role in the primary humoral response of the immune system. This review article reviews the biological properties of IgM, modern epidemiology (including the increase in the disease in the younger population), pathogenetic mechanisms (MYD88 L265P, CXCR4 mutations, cryoglobulinemia, autoimmune regulation), diagnostic approaches (immunofixation, NGS, cryoglobulin detection), and the latest treatment strategies (BTK inhibitors, BCL2 inhibitors, rituximab, plasmapheresis, CAR-T and bispecific antibodies). Special attention is paid to the significant increase in Waldenström macroglobulinemia and IgM-related cryoglobulinemia in young patients (up to 50 years old) over the past 5 years, as well as post-COVID-19 autoimmune syndromes. The article is intended for hematologists, immunologists, and internal medicine physicians.

Immunoglobulin M. Waldenström macroglobulinemia, MYD88 L265P, cryoglobulinemia, BTK inhibitors, rituximab, plasmapheresis, selective IgM deficiency.

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