title: The role of CD4 in antigen-independent activation of isolated single T lymphocytes.
abstract: The membrane molecule CD4 (L3T4) is thought to facilitate activation of Class II H-2-restricted T cells by binding to Ia determinants on antigen-presenting cells. Recent reports suggest that CD4 can also contribute to antigen-independent activation by anti-T cell receptor (TCR) antibodies. An assay which measures the secretion of two lymphokines, granulocyte-macrophage colony-stimulating factor and interleukin 3 (IL-3), by single T cells activated with an anti-TCR antibody, F23.1, was used to analyze the effects of anti-CD4 antibodies on antigen-independent T cell activation. Single cells of a CD4+F23.1+ clone were micromanipulated into wells to which F23.1 had been immobilized, and their lymphokine secretion was measured 24 hr later. The frequency of lymphokine-secreting cells was consistently reduced up to 10-fold in the presence of soluble anti-CD4 antibody (GK1.5) but only up to 2.5-fold by an antibody to the cell adhesion molecule, LFA-1. In both bulk and single-cell cultures, responses to suboptimal concentrations of F23.1 were more susceptible to inhibition by GK1.5 than responses to optimal F23.1. The failure of GK1.5 to inhibit IL-2-stimulated lymphokine synthesis in bulk cultures suggested that CD4 ligation did not deliver a negative signal to the clone. By contrast, when either anti-CD4 or anti-LFA-1 was immobilized on the same surface as F23.1, the frequency of lymphokine-secreting cells could be increased up to 10-fold. It is concluded that anti-CD4 antibodies can act directly on the responding T cell to affect TCR-dependent activation, in the absence of interaction with antigen-presenting cells or any other cell type.
mesh_terms: D000911:Antibodies, Monoclonal; D000937:Antigen-Antibody Reactions; D000943:Antigens, Differentiation / Q000276:immunology; D000945:Antigens, Differentiation, T-Lymphocyte / Q000276:immunology*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D002478:Cells, Cultured; D002999:Clone Cells; D003115:Colony-Stimulating Factors / Q000096:biosynthesis; D006801:Humans; D066298:In Vitro Techniques; D008213:Lymphocyte Activation; D016169:Lymphocyte Function-Associated Antigen-1; D008222:Lymphokines / Q000096:biosynthesis*; D012995:Solubility
chemical_list: D000911:Antibodies, Monoclonal; D000943:Antigens, Differentiation; D000945:Antigens, Differentiation, T-Lymphocyte; D003115:Colony-Stimulating Factors; D016169:Lymphocyte Function-Associated Antigen-1; D008222:Lymphokines