has plasma membrane part capable of has high plasma membrane amount mature B cell B-1 B cell There are small numbers of B-1 cells found in the lymph nodes and spleen, while larger numbers can be found in the peritoneal and pleural cavities. B-1 B cells are reportedly CD11b-positive, CD20-positive, CD21-positive, CD27-positive, CD44-positive, CD45RB-positive, CD48-positive, CD70-negative, CD150-positive, CD244-negative, CD352-positive, sIgM-positive, and sIgD-low. B1 B cell B-1 cell B1 B-lymphocyte A B cell of distinct lineage and surface marker expression. B-1 B cells are thought to be the primary source of natural IgM immunoglobulin, that is, IgM produced in large quantities without prior antigenic stimulation and generally reactive against various microorganisms, as well as the source of T-independent IgA immunoglobulin in the mucosal areas. These cells are CD43-positive. B-1 B-lymphocyte B-1 B cells represent a unique subset of B lymphocytes distinguished by their functional and phenotypic characteristics. These cells have been well studied in mice, though their human counterparts remain more difficult to characterize. These cells are predominantly found in the peritoneal and pleural cavities and play a crucial role in the body's immune response, being a part of the adaptive immune system. They are significant producers of natural antibodies even in the absence of an identifiable pathogen, making them a pivotal link between the innate and adaptive immune responses. They can be further subdivided into B-1a and B-1b cells. One of the defining features of B-1 B cells is the innate-like pattern of their immune response. Unlike conventional B cells (B-2 cells), which require interaction with T helper cells to initiate antibody production, B-1a B cells respond rapidly to microbial challenges, with an immediate production of low-affinity, polyreactive antibodies. These antibodies readily bind to various pathogens and provide an immediate first line of defence against invading microbes. In addition to their protective role, these antibodies also play a crucial part in maintaining homeostasis by facilitating the clearance of cellular debris and apoptotic cells. However, these antibodies can also be autoreactive and contribute to autoimmunity. Meanwhile, B-1b cells appear to produce antibodies specific to T-independent antigens. Moreover, B-1 B cells possess the unique ability to self-renew, akin to stem cells. This distinctive property contrasts with conventional B-2 cells, which are replenished by the bone marrow. Whereas B-2 cells primarily contribute to secondary antibody responses, B-1 B cells are known for their role in primary and early secondary immune responses. By exhibiting characteristics of both innate and adaptive immunity, B-1 B cells bridge the gap between these two divisions of the immune system, providing comprehensive protection against pathogens while maintaining body homeostasis. (This extended description was generated by ChatGPT and reviewed by the CellGuide team, who added references, and by the CL editors, who approved it for inclusion in CL. It may contain information that applies only to some subtypes and species, and so should not be considered definitional.) B1 B-cell B1 cell B1 B lymphocyte B-1 B lymphocyte https://cellxgene.cziscience.com/cellguide/CL_0000819 B-1 B-cell innate immune response IgM immunoglobulin complex receptor-type tyrosine-protein phosphatase C isoform CD45RABC membrane-spanning 4-domains subfamily A member 1 leukosialin