Analysis of molecular structures of B cell differentiation factors and the corresponding receptors, and their functions.

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1) Molecular properties of two distinct B cell differentiation factors produced from B151K12 T cell hybridoma: The B151-TRF1, which induces differentiation of antigen-activated B cells into antibody-forming cells, is a hydrophobic glycoprotein bearing sialic acid and N-acetylgalactosamine (Ga1NAc) with an apparent m.w. of 50,000 by gel-permeation and 19,000 by SDS-PAGE and PI 4.9 - 5.1. The B151-TRF2, which induces polyclonal B cell differentiation of unprimed B cells, is a non-glycosylated protein with an apparent m.w. of 30,000 by gel-permeation and PI 4.3 - 4.5. The B151-TRF2 is more hydrophobic than B151-TRF1, and inactivated by heat-treatment (56゜C 30') in contrast to heat-stable B151-TRF1. In addition, B151-TRF2 has affinity for N-acetylglucosamine (G1cNAc).2) By taking advandtage of the fact that mutant DBA/2Ha mice lack B cells expressing B151-TRF1-receptor in an X-linked recessive manner, a monoclonal antibody specific for B151-TRF1receptor was obtained from a hybridoma establ … More ished from B cells of TRF1-low responder (DBA/2HaxBALB/c)F1 male mice immunized with high-responder BALB/c B cells. It was revealed that B151-TRF1-receptor is a glycoprotein containing mannose residues with m.w. of 120,000, which consists of a disulfide-linked homodimer of a glycoprotein with m.w. of 60,000. On the other hand, B151-TRF2-receptor is a glycoprotein with N-terminal G1cNAc residues as revealed by analysis of B151-TRF2-absorbing ability of B cells after treatment wih proteinase or glycosidase. Interestingly, CBA/N B cells bearing ax X-linked immune defect failed to respond to both B151TRFs, irrespective of normal expression of respective receptors. In contrast, DBA/2Ha B cells responded to B151-TRF2 but not B151-TRF1 by virtue of the absence of B151-TRF1-receptor.3) It was demonstrated that Ga1NAc residues on B151-TRF1 molecule plays an important role in binding of B151-TRF1 molecule to the receptor, whereas recognition by B151-TRF2 of G1cNAc residues on B151-TRF2-receptor is required for B cell activation. Less