Defective secretion of an immunoglobulin caused by mutations in the heavy chain complementarity determining region 2.
We have investigated four secretion-deficient antibodies (Abs) derived from a panel of 46 mutant T15 anti-phosphocholine Abs, all of which have point mutations in the heavy chain (H) complementarity determining region 2 (CDR2). The level of secretion for these four Abs was < 10% of wild type when expressed together with the T15 light chain (L) in either SP2/0 or P3X63Ag8.653 myeloma cells although normal levels of H and L chain mRNA were produced. Moreover, abundant intracellular H and L chain proteins were detected. Three of the four mutants had little or no assembled H and L complexes intracellularly whereas one had a significant amount of intracellular immunoglobulin (Ig) which was shown to be capable of binding Ag. Thus, we demonstrate for the first time that point mutations confined to CDR2 of the H chain variable (V) region can impede Ab assembly and secretion. We then introduced the same CDR2 mutations into a related H chain which is encoded by the same T15 VH gene but different diversity (D) and joining (J) genes. When these H chains were expressed with a non-T15 L chain, the resulting Abs were secreted normally. The results thus suggest that the effects of the CDR2 mutations on Ab secretion are dependent on their interactions with L and/or H chain D-J sequences. These results also reveal a novel mechanism that could contribute to B cell wastage.
Chen
C
C
Department of Microbiology and Immunology, Oregon Health Sciences University, Portland 97201.
Martin
T M
TM
Stevens
S
S
Rittenberg
M B
MB
D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D003001:Cloning, Molecular; D004797:Enzyme-Linked Immunosorbent Assay; D007143:Immunoglobulin Heavy Chains / Q000235:genetics* / Q000276:immunology; D007135:Immunoglobulin Variable Region / Q000235:genetics* / Q000276:immunology; D007136:Immunoglobulins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D010767:Phosphorylcholine / Q000276:immunology; D017354:Point Mutation
D007143:Immunoglobulin Heavy Chains; D007135:Immunoglobulin Variable Region; D007136:Immunoglobulins; D010767:Phosphorylcholine