Figure 2

The stimulation of the undifferentiated CD4+ T-helper cell by signals delivered to the T-cell receptor (Signal 1), by cell-to-cell-contact (Signal 2), and by soluble signals (Signal 3) from the dendritic cells or other adjacent cell types. The signalling molecule pairs (with the relevant receptor on the T-cell mentioned first) are but a few examples of those described in the literature.