Characterization of the physical interaction between antigen-specific B and T cells.

TLDR

Physical interaction between antigen‑specific B cells and helper T cells is an early essential step in the antibody response to thymus‑dependent antigens. The study examined B‑T cell interaction using carrier‑specific T hybridoma cells to help highly enriched hapten‑binding B cells. B cells incubated with antigen for 4–6 h then form conjugates with T cells within 5 min, a process requiring hapten and carrier specificity, covalent hapten‑carrier linkage, and MHC restriction, and can be visualized and quantified by light and electron microscopy. Electron microscopy revealed antigen‑independent microvilli attachment and antigen‑dependent intimate apposition between B and T cells; the latter’s increasing frequency over time suggests a role in signal transduction, and blocking antibodies against Thy‑1.2, LFA‑1α, L3T4, and I‑A partially inhibit conjugation, implicating these surface molecules.

Abstract

Abstract It has been assumed that physical interaction between B cells and helper T cells in the presence of specific antigen is an early and essential step in the physiologic antibody response to thymus-dependent antigens. The present studies were designed to examine this physical interaction by employing carrier-specific T hybridoma cells that can provide help to highly enriched hapten-binding B cells. Direct conjugation of the B and T cells can be visualized at both the light and electron microscopic level and the number of conjugates can be directly quantified. Before their effective conjugation with T cells, the B cells must be incubated with specific antigen for 4 to 6 hr. After this time, the T cells form conjugates with the B cells within 5 min. Conjugate formation requires hapten specificity, carrier specificity, covalent linkage between hapten and carrier, and is MHC restricted. Two types of T-B conjugates were observed by electron microscopy: an antigen-independent attachment of B cell microvilli to small portions of the T cell surface and an antigen-dependent, intimate apposition of large areas of the plasma membranes of the T and B cells. The kinetics of development of the two modes of interaction suggest that the second type may be important for signal transduction, since the number of T and B cells showing intimate interactions increases with time. Monoclonal antibodies directed against Thy-1.2, LFA-1 alpha, L3T4, and I-A partially block conjugation of the two cell types, suggesting that these surface molecules are involved in T-B interaction.