lacks_plasma_membrane_part B-1 B cell B-1b B cell B1b B lymphocyte B-1b B cells are a subtype of B cells, which are part of the humoral immune system. B cells can be divided into B-1 and B-2 cells, and B-1 cells can be further subdivided into B-1a and B-1b cells. B-1b B cells are especially abundant in the pleural and peritoneal cavities in humans and mice, and they differ from B-1a B cells in that they lack the expression of the surface molecule CD5. Functionally, B-1b B cells are vital players in the immune response, particularly in providing defense against pathogens. They appear to specialize in recognizing T-independent, pathogen-associated antigens. B-1b B cells can respond to these antigens by rapidly proliferating and differentiating into cells capable of producing natural antibodies, primarily of the IgM class. These antibodies are of low affinity but broad specificity, allowing for the rapid targeting of a wide range of pathogens before the adaptive immune response has fully developed. These cells, unlike B-1a B cells, appear to undergo clonal expansion in response to antigen exposure. B-1b B cells are also thought to contribute to immunological memory. (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.) B1b B cell B1b cell B1b B-lymphocyte https://cellxgene.cziscience.com/cellguide/CL_0000821 B-1b B-cell B-1b B lymphocyte B-1b B-lymphocyte A B-1 B cell that has the phenotype CD5-negative, but having other phenotypic attributes of a B-1 B cell. B1b B-cell T-cell surface glycoprotein CD5