Human CD8+ memory- and effector-type T cells are poorly defined. We show here that, next to a naive compartment, two discrete primed subpopulations can be found within the circulating human CD8+ T cell subset. First, CD45RA−CD45R0+ cells are reminiscent of memory-type T cells in that they express elevated levels of CD95 (Fas) and the integrin family members CD11a, CD18, CD29, CD49d, and CD49e, compared to naive CD8+ T cells, and are able to secrete not only interleukin (IL) 2 but also interferon γ, tumor necrosis factor α, and IL-4. This subset does not exert cytolytic activity without prior in vitro stimulation but does contain virus-specific cytotoxic T lymphocyte (CTL) precursors. A second primed population is characterized by CD45RA expression with concomitant absence of expression of the costimulatory molecules CD27 and CD28. The CD8+CD45RA+CD27− population contains T cells expressing high levels of CD11a, CD11b, CD18, and CD49d, whereas CD62L (L-selectin) is not expressed. These T cells do not secrete IL-2 or -4 but can produce IFN-γ and TNF-α. In accordance with this finding, cells contained within this subpopulation depend for proliferation on exogenous growth factors such as IL-2 and -15. Interestingly, CD8+CD45RA+CD27− cells parallel effector CTLs, as they abundantly express Fas-ligand mRNA, contain perforin and granzyme B, and have high cytolytic activity without in vitro prestimulation. Based on both phenotypic and functional properties, we conclude that memory- and effector-type T cells can be separated as distinct entities within the human CD8+ T cell subset.

A new monoclonal antibody, MOMA-2, is described, which recognizes monocytes and macrophages in the mouse. The antibody reacts with the majority of mononuclear phagocytes in various tissues as determined by immunohistochemistry. It differs from other macrophage markers that have been described by the strong reaction with macrophages in the lymphoid organs such as the tingible body macrophages and macrophages in T cell-dependent areas. The antibody recognizes predominantly a cytoplasmic component, although a membrane component can also be demonstrated. Isolated Langerhans' cells, interdigitating cells and dendritic cells, members of the mononuclear phagocyte system that are involved in antigen presenting, stain weakly with the antibody. Because of the intense staining the antibody is very useful for defining tissue macrophages by immunohistochemistry.

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CD4

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The finding of seasonal variation of immune function in serially MRI-monitored MS patients suggests an environmental role in T-cell activation.

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