B lymphocyte differentiation in the rat: production and characterization of monoclonal antibodies to B lineage‐associated antigens

Abstract

Three mouse monoclonal antibodies (mAb) directed against rat B lineage antigens were produced. The mAb, designated HIS14 (IgG₁), HIS22 (IgM) and HIS24 (IgG_2b), were characterized for binding to lymphoid and nonlymphoid tissues by immunoperoxidase staining of frozen sections and by (double‐) immunofluorescence staining of single cell suspensions from lymphoid organs. HIS14 recognized a pan B cell determinant: it reacted with virtually all cells of each anatomic B cell compartment and with about 95% of surface (s)Ig⁺ cells in thoracic duct lymph and in suspensions of spleen and lymph nodes. HIS22 and HIS24 detected B lineage‐associated antigens expressed by major subpopulations of B cells. HIS22 predominantly stained the lymphocyte corona, but not (or weakly) the germinal centers and splenic marginal zones, whereas HIS24 reacted with both corona and germinal center and not (or weakly) with marginal zone. In accordance with this, substantial proportions of sIg⁺ cells in spleen cell suspensions did not express HIS22 or HIS24 determinants (20% and 27%, respectively). In bone marrow the vast majority of cytomplasmic μ⁺ pre‐B cells were HIS14⁺ and HIS24⁺, and up to one third also HIS22⁺, indicating an appearance of the determinants early in B lymphocytopoiesis. The antigens recognized by HIS14, HIS22 and HIS24 are lost during the final stage of B cell differentiation: none of the mAb bound to plasma cells. As far as detectable, neither cells of myeloid and erythroid lineages in bone marrow nor thymocytes were stained by HIS14, HIS22 or HIS24. In suspensions of peripheral lymphoid organs (spleen and lymph nodes) but not in thoracic duct lymph, HIS14 and HIS24 labeled a small proportion (12% and 14%, respectively) of Ig⁻ cells. HIS22 did not bind to Ig⁻ peripheral lymphocytes. Reactivity of HIS14, HIS22 and HIS24 with nonlymphoid tissues was virtually absent; HIS22 stained the high endothelial venules in lymph nodes and Peyer's patches. As determined by immunoblotting, the antigenic determinants on lymph node cells recognized by HIS14, HIS22 and HIS24 were present on molecules with an apparent molecular mass of 205 kDa, 210 (and 175) kDa and 205 kDa, respectively, which is similar to the molecular mass of the B cell form of the rat leukocyte common antigen. In addition, the antigens recognized by HIS14, HIS22 and HIS24 co‐capped with the leukocyte common antigen. This suggests that each of the three mAb recognize determinants present on the B cell form of the leukocyte common antigen.