Antigen Presenting Cells: Not T Cells

[justadream]

From my reading, it appears that B-cells, macrophages, and dendritic cells are the 3 main types of antigen-presenting cells (APC).

This would imply that T-cells are not antigen presenting.

I understand why macrophages and dendritic cells are antigen-presenting. But why is it that B-cells are but T-cells are not (in terms of their function/role in the immune system)?

---

Members don't see this ad.

 

[Czarcasm]

From my reading, it appears that B-cells, macrophages, and dendritic cells are the 3 main types of antigen-presenting cells (APC).

This would imply that T-cells are not antigen presenting.

I understand why macrophages and dendritic cells are antigen-presenting. But why is it that B-cells are but T-cells are not (in terms of their function/role in the immune system)?

The reason is because only those 3 types of cells you mentioned (B cells, Dendritic Cells, and Macrophages) have MHC II on their PM's. As an APC, these cells ingest the antigen, degrade it, and place a piece of the antigen on the MHC II for presentation so that it could be recognized by CD4+ T Cells. Generally though (as presented in most Immunology courses), the main APC of the 3 are Dendritic Cells. These cells are recruited to an area of infection by macrophages and after obtaining an antigen via phagocytosis, they stop their phagocytotic activity and increase synthesis of MHC I and MHC II receptors, then begin traveling towards a lymph node where immature T cells reside. From there, they (are strong enough to) activate both CD4+ T cells (via MHCII-antigen) and CD8+ T cells (via MHCI-antigen) simulatenously, in the lymph nodes. Once these immature T cells are selected for, they can begin activating immature B cells who also reside in the lymph node. These immature B cells briefly mature to IgM secreting plasma cells, but as they migrate to the cortex of the lymph node, they differentiate via different mechanisms to high affinity IgA, IgG, IgE secreting plasma cells. (The isotype switching process is regulating by the helper cell assisting in this process via cytokines). Bare in mind that while some immature B cells differentiate to plasma cells, memory cells are also formed in the process (though these don't differentiate to plasma cells unless stimulated upon re-exposure). This is essentially the whole process in a nutshell. Also note, the general process of B cell activation described above (using dendritic cells as an APC) can also apply to B cells and Macrophages; however this is generally not the case as these cells aren't "strong enough" to activate naive T cells to the same extent dendritic cells do.