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The book I'm studying says the following "During a cell mediated immune response, the release of IL-2 by helper T-cells is resposible for stimulating the production of Cytotoxic T-cells, which have receptors that match the anti-gen of the infecting pathogen."

I'm not exactly sure if this is impliying that cytotoxic T-cells are only produced and present during an immune response or not, since I also have an older version of the book that simply says "the IL-2 released by helper T-cells activates cytotoxic T-cells" which seems to indicate that they are normally always present, but just inactive

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Naive T cells are regularly matured in the thymus where they're released into the blood. A majority are CD4+, but many are also CD8+. As a caveat, many are TCRαß+, and few are TCRyδ+ (outside the scope here but fun to look up and read). From there, they home to the lymph node where they hang in the T cell zone until blood trafficking signals coax them into the blood. T cells regularly navigate the body in response to signals from different cells such as blood vessel endothelium, lymphaptic vessel endothelium, epithelial cells, and so forth (1).

The basic process behind an adaptive immune response is that antigen-presenting cells get ahold of foreign antigens and head back to the lymphoid organs like lymph nodes. By the time they get there, they've matured into "licensed" professional antigen-presenting cells. They interact with both CD4+ or helper T cells, and CD8+ or cytotoxic T cells. It's more complex than that, but the point of the helper T cell is to produce "help" signals. These include IL-2, and other cytokines which not only assist the CD8+ T cells in their activation, but also determine a lineage they'll take based on other factors.

So they're both there, in the lymph node at the time the antigen-presenting cell, such as a dendritic cell, arrives to activate the lymphocytes in that region. Take home point: the naive lymphocytes are there until they are activated, in which you would be correct in your last line. But they do actually do things other than sit there, other take home point. They aren't simply anergic and waiting.

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  • $\begingroup$ By other things, do you mean seeking and killing cancer cells and foriegn tissues and parasites (though these two I think could be the same thing as just an immune response, since they're foriegn) ? That's also breifly mentioned but just that, it isn't talked about much. $\endgroup$ – Dahen Apr 26 '18 at 21:32
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    $\begingroup$ Well to be certain, cancer cells are subject to immunoediting, which is another complex term you can look into. There are also things handled by innate immunity and B cells. The naive T cells, however, can extravasate into tissues secreting chemokines in response to say, a pathogen. There are intra-epithelial lymphocytes and dendritic cells and macrophages that hang out in tissues like the gut mucosa and have the potential to active lymphocytes in situ. So "other things" can mean a great deal of things. $\endgroup$ – CKM Apr 27 '18 at 1:45

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