FIG. 1.

Activation of T cells by HTLV-I. Infection of CD4⁺ T cells influences immune system T-cell activation by at least four separate pathways. (i) The HTLV-I-infected T cells are activated by viral interference with signaling pathways and transcriptional regulation (bottom right). (ii) The HTLV-I-infected T cell interacts with and activates resting T cells (top right, activation of uninfected T cells) in a viral antigen-independent manner. The CD58-CD2 interaction (shown) is critical, but other molecular interactions and cytokines (not shown) are likely to contribute. (iii) Virus-specific CD8⁺ T cells (and, to a lesser degree, CD4⁺ T cells [not shown]) are activated by recognition of viral peptide epitopes (bottom left, antigen-specific activation of CD8⁺ T cells). (iv) APC may present MHC class II-restricted peptide antigens that activate the HTLV-I-infected T cell (top left, antigen-specific activation of HTLV-I-infected T cells). This activation process is altered by virtue of viral interference with the signaling cascade or the transcriptional regulation of the HTLV-I-infected T cell, or both.