Blocking and Redistribution ("Capping") of Antigen Receptors on T and B Lymphocytes by Anti-Immunoglobulin Antibody

Abstract

Antigen-binding T and B lymphocytes were studied by combined autoradiography and immunofluorescence; mouse spleen lymphocytes binding the antigens, [125I]MSH or [125I]TIGAL, were incubated with rhodamine-labeled anti-Ig reagents or with a rhodamine-labeled IgG fraction of anti-θ serum. B cells were identified as Ig+ or θ-, T cells as Ig- or θ+. It was found that: (a) 20% (1–2 mo after priming) to 30% (3.5–4 mo after priming) of the antigen-binding cells were T cells. (b) The range of antigen molecules bound by B and T cells was similar. (c) Binding of antigen to B and T cells was inhibited by polyvalent anti-Ig, anti-µ, or anti-L reagents. Binding to T cells was more readily inhibited than to B cells. Normal rabbit serum, antimouse lymphocyte serum, or anti-θ did not inhibit antigen binding. (d) When Ig at the surface of B cells was induced, by noninhibiting concentrations of anti-Ig reagents, to redistribute into polar caps and the cells subsequently exposed to [125I)antigen under noncapping conditions, the [125I]antigen silver grains were distributed in caps superimposed on the Ig fluorescent cap. Of crucial importance, antigen was found in cap in the same proportion of T cells as B cells. Significant capping of antigen receptors was not induced in B or T cells with normal rabbit serum or by anti-Ig reagents absorbed with mouse Ig. The main conclusions of this series of experiments using direct visualization of antigen-binding B and T lymphocytes is that T cells have antigen-specific receptors, probably of IgM nature, and that the number of these receptors appears to range in the order of thousands.

CD8 T Cells, Like CD4 T Cells, Are Triggered by Multivalent Engagement of TCRs by MHC-Peptide Ligands but Not by Monovalent Engagement

“…The following peptides were all synthesized using 9-fluorenylmethoxycarbonyl chemistry and verified using mass spectrometry: SIY (SIYRYYGL) found from a combinatorial library to activate the 2C TCR in complex with H2-K b (22); OVA (SIINFEKL) derived from OVA; QL9 (QLSPFPFDL) modified from an endogenous murine peptide presented on H2-L d ; influenza hemagglutinin (HA) 3 (PKYVKQNTLKLAT); and A2 (VGSDWRFLRGYHQYA) derived from the human class I MHC allele HLA-A2. For use in direct treatment of T cells or in making soluble class II MHCs, the peptides were purified using reverse-phase HPLC; crude peptide was used for refolding into soluble class I MHCs.…”

“…However, despite much work in this area, the specific molecular event that is detected by the T cell upon Ag-specific TCR engagement has been difficult to identify. In other immune cells such as B cells or mast cells in which the Ag recognized is a soluble particle, multivalent receptor engagement has been observed to be crucial for stimulation (1)(2)(3). Conversely, T cells are triggered by antigenic stimuli presented on the surface of another cell, and the specific interaction is accompanied by a multitude of non-Ag-specific interactions including: binding of adhesion molecules, engagement of costimulatory receptors, possible contributions of nonstimulatory MHC-peptide complexes, and MHC coreceptor binding.…”

Function of Macrophages in Antigen Recognition by Guinea Pig T Lymphocytes

“…Antigen binding to T cells has been measured indirectly by exposing cells in vitro to [12~I]-antigen of high specific activity with subsequent killing or "suicide" of the specific antigen-binding T lymphocytes (9). More recently, theta-positive, surface immunoglobulin-negative antigen-binding cells have been visualized directly after incubation of primed mouse spleen cells with relatively high concentrations of 125I-labeled antigen (10) and by the cytoadherence techniques (11).…”

Soluble peptide–MHC monomers cause activation of CD8+T cells through transfer of the peptide to T cell MHC molecules

“…This concept arose largely from observations of antigen-induced capping of surface immunoglobulins on B cells (1,2) and multivalent antigen triggering of histamine release from mast cells (3). Whether multivalent engagement of T cell antigen receptors (TCR) is required to initiate T cell activation has been difficult to determine, primarily because the antigens are peptide-MHC complexes normally found as integral membrane proteins on the surfaces of other cells.…”