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. innate immune response IgM immunoglobulin complex receptor-type tyrosine-protein phosphatase C isoform CD45RABC membrane-spanning 4-domains subfamily A member 1 leukosialin