title: Limiting dilution analysis of alloreactive T helper cells: precursor frequencies similar to that of alloreactive cytotoxic T cells.
abstract: Precursor frequencies for alloreactive T helper cells involved in the generation of primary cytotoxic responses from thymocytes were determined in splenic T cells and selected Lyt-1 lymphocytes by limiting dilution analysis. T helper precursors at frequencies ranging from 1/5000 to 1/13,500 were found in individual experiments in unsensitized selected Lyt-1 populations reacting to H-2 alloantigens. After preactivation of Lyt-1 lymphocytes with antigen in limiting dilution, the frequencies of T helper cells were increased 2-3 fold when cultured in the absence and 10-50-fold when cultured in the presence of T cell growth factor. The frequencies for T helper precursors found in Lyt-1 cells were comparable to those of unselected T cells, indicating that a significant portion of T helper cells resides in the Lyt-123 population. Activation of T helper precursors with H-2 antigens or with H-2 and non-MHC (plus MLs) antigens resulted in similar frequencies, suggesting that the same T cell can respond to H-2 and non-MHC determinants. The data suggest that alloreactive T helper precursors exist at frequencies similar to that of CTL precursors. In addition, the results indicate that the induction of CTL by T helper cells is subject to regulation presumably by suppressive cells and that Lyt-1 inducer cells may be involved in the development of suppression for CTL responses.
mesh_terms: D000818:Animals; D000950:Antigens, Ly / Q000032:analysis; D002454:Cell Differentiation; D007958:Leukocyte Count; D051379:Mice; D013154:Spleen / Q000166:cytology; D013602:T-Lymphocytes, Cytotoxic / Q000166:cytology; D006377:T-Lymphocytes, Helper-Inducer / Q000166:cytology / Q000276:immunology*
chemical_list: D000950:Antigens, Ly