Mechanisms of the initiation and regulation of immune responses by accessory cells

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Initiation of T cell responses depends on the air of non-T Ia-bearing cells generally called "accessory cells (A-cells)". We have so far elucidated that the resting T cells are activated only by the aid of dendritic cells (DC), but once activated T blastoid cells become responsive to Ia^+ macrophages (M<phi>) and also to B cells. In these two years, we have investigated mechanisms of the initiation and regulation of T cell responses by A-cells, and obtained the results below.1. Ia expression on M<phi> of infant animals is suppressed fby their autocrine of interferonbeta.2. Functonal decline of dendritic cells with ageing is different among mouse strains.3. The enhancing effect of M<phi> on mixed leukocyte reaction, primary antibody respones, and secondary proliferative response of immune T cells is mediated by IL-1 and GM-CSF which are produced by M<phi> themselves. The garget of these factors is DC but not T cells.4. Neuraminidase-treated M<phi> induce cytotoxic T lymphocytes from CD4^-8^+ cells in the presence of IL-2 without the help of CD4^+8^- T cells. The presence of Ia^+ A-cells is not required.