The CD150 receptor is expressed on thymocytes, activated and memory T cells, B cells, platelets, natural killer T cells, and mature dendritic cells, and is also detected on tumor cells of Hodgkin's lymphoma (HL) and diffuse large B-cell lymphoma with an activated B cell phenotype. Here, we report that the level of CD150 expression is elevated during B cell differentiation toward plasma cells. In primary tonsillar B cells and HL cell lines, CD150 signaling regulates the phosphorylation of three types of mitogen-activated protein kinases (MAPKs): extracellular signal-regulated kinase 1/2 (ERK1/2), p38 MAPK, and Jun N-terminal kinase 1/2 (JNK1/2). CD150 induced ERK1/2 activation in primary tonsillar B cells and in two HL cell lines. CD150 mediated activation of JNK1/2 p54 and JNK2-gamma kinase isoforms in all CD150(+) B cell lines we tested. CD150 associated with the serine/threonine kinase hematopoetic progenitor kinase 1 (HPK1) regardless of CD150 tyrosine phosphorylation or binding of the SH2D1A adaptor protein to CD150, and HPK1 overexpression enhanced CD150-mediated JNK1/2 phosphorylation. CD150 ligation inhibited cell proliferation of all studied HL cell lines and induced apoptosis in L1236 HL cells that did not depend on JNK activity. As signaling through CD150 modulates MAPK activity in HL tumor cells, CD150 may contribute to regulation of tumor cell maintenance in low-rate proliferating HLs.