T cells attack foreign cells and T helper cells secrete substances (cytokines) that activate the T cells. This is good for autoimmune diseases. Not good for HIV/AIDS due to the fact that this virus attacks T helper cells. As for allergies, many different pathways mediate an allergic reaction, most of which are not fully understood. Immunoglobulins are involved, for instance IgE. If you have an increase in IgE, this can cause skin reactions/hives, etc. This is linked to an increase in the amount of basophils in the peripheral blood pool. Basophils have IgE on the surface and cause an increase of histamine. (which is why people take ANTI-histamines.) Mast cells are also involved in releasing histamine, but they like to stay in the bone marrow. I don't remember them doing too much unless they spill out into the peripheral blood pool.
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T cells attack foreign cells and T helper cells secrete substances (cytokines) that activate the T cells. This is good for autoimmune diseases. Not good for HIV/AIDS due to the fact that this virus attacks T helper cells. As for allergies, many different pathways mediate an allergic reaction, most of which are not fully understood. Immunoglobulins are involved, for instance IgE. If you have an increase in IgE, this can cause skin reactions/hives, etc. This is linked to an increase in the amount of basophils in the peripheral blood pool. Basophils have IgE on the surface and cause an increase of histamine. (which is why people take ANTI-histamines.) Mast cells are also involved in releasing histamine, but they like to stay in the bone marrow. I don't remember them doing too much unless they spill out into the peripheral blood pool.