... of class II histocompatibility molecules. Only specialized antigen-presenting cells express class II molecules. These include:dendritic cells, phagocytic cells like macrophages and B cells! CD8+ T cells The best understood CD8+ T cells are cytotoxic T lymphocytes (CTLs). They secrete molecules that destroy the cell to which they have bound. This is a very useful function if the target cell is infected with a virus because the cell is usually destroyed before it can release a fresh crop of virus particles that leave the cell (often killing it in the process) and spread to new target cells. Class I and class II molecules present antigen fragments to different subsets of T cells. Most of the T cells of the body belong to one of two distinct subsets: CD4+ or CD8+. CD4 and CD8 are surface glycoproteins. Both CD4+ and CD8+ T cells have an antigen receptor (TCR) that "sees" a complex histocompatibility molecule. However, ...

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