Coclustering of CD4 (L3T4) molecule with the T-cell receptor is induced by specific direct interaction of helper T cells and antigen-presenting cells.

Blocking studies with monoclonal antibodies have suggested that helper T cell recognition and triggering involve the CD4 (L3T4) accessory molecule as well as the T-cell receptor (TCR) that is linked to the T3 complex. We have investigated the surface distribution of L3T4 and TCR during the direct interaction of a cloned murine helper T-cell line with an antigen-presenting B-cell line. Using immunofluorescence microscopy, we show that in 1:1 cell couples formed between the two cells, in which a specific interaction can be demonstrated, the L3T4 and the TCR become redistributed on the T-cell surface so that they are concentrated in the cell-cell contact region. This coclustering of L3T4 with TCR occurs only when the relevant antigen and appropriate major histocompatibility class II molecules are presented to the T cell, and it therefore requires the specific interaction of the TCR with its complex ligand on the antigen-presenting cell.