B cell responses to a peptide epitope: III. Differential T helper cell thresholds in recruitment of B cell fine specificities.
Th cell requirements in the individual stages comprising a murine humoral response to a synthetic peptide were examined. Induction of a T-dependent IgM response was readily achieved in the presence of unprimed or low numbers of Ag-primed T cells. In contrast, class switch to the IgG isotype of Abs demanded a markedly elevated frequency of primed T cells and occurred concomitantly with B cell differentiation into an membrane-bound IgG+ memory population. These results indicated that induction and progression of a T-dependent humoral IgG response were comprised of a single rate-limiting step represented by that involving Ab isotype switch. Subsequent studies established that this also represented the principal step where antibody-purifying mechanisms operate. This was enforced by imposing a threshold barrier for Th cell recruitment by early Ag-activated B cells to enable class switch and consequent retention as the response progresses. The quantum of this threshold, however, was not invariant, but, rather, was described as a balance between the affinity of B cell receptor for Ag and the frequency of Ag-specific Th cells.
Agarwal
A
A
Immunology Group, International Center for Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, New Delhi, India.
Rao
K V
KV
D000276:Adjuvants, Immunologic / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D000918:Antibody Specificity; D001402:B-Lymphocytes / Q000276:immunology*; D002352:Carrier Proteins / Q000276:immunology; D005260:Female; D007114:Immunization; D016056:Immunodominant Epitopes / Q000276:immunology*; D017578:Immunoglobulin Class Switching; D007074:Immunoglobulin G / Q000096:biosynthesis; D007132:Immunoglobulin Isotypes / Q000096:biosynthesis; D007075:Immunoglobulin M / Q000096:biosynthesis; D008213:Lymphocyte Activation; D051379:Mice; D008807:Mice, Inbred BALB C; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000276:immunology* / Q000494:pharmacology; D006377:T-Lymphocytes, Helper-Inducer / Q000276:immunology*
D000276:Adjuvants, Immunologic; D002352:Carrier Proteins; D016056:Immunodominant Epitopes; D007074:Immunoglobulin G; D007132:Immunoglobulin Isotypes; D007075:Immunoglobulin M; D010455:Peptides