Respond to the following:
Acquired immune responses are capable of controlling aninfection, however, the acquired immune response is controlleditself through different mechanisms. It is primarily activated by athreshold level of antigen that is produced through the defensiveaction of the innate immune system. Pathogens and antigens interactand cause dendritic cells to activate to become antigen-presentingcells. Then, the antigens are transported to the lymphoid organs bythe antigen-presenting cells. After several days, antigen-specificT cells and B cells locate the foreign antigen, and ultimatelydifferentiate into armed effector cells. These cells either leavethe lymphoid organ to go to the sites of infection or stay withinthe organ to promote humoral immunity. The path the effector cellstake is dependent on the differentiation of CD4 T cells. There aretwo different subsets of CD4 T cells, Th1 and Th2. The function ofTh1 is to activate macrophages, while Th2 works to activate Bcells, especially during the primary response. Both of these CD4 Tcell subset are capable of regulating each other, which isessential done by the cytokines of each respective T cell type.Ultimately, the effector cells remove the pathogens to control theinfection (1). Once an infection is effectively under control, itis critical to remove the effector cells to allow for therestoration of the tissue. The immune system has mechanisms inwhich it is capable of removing these cells. When effector cellsare no longer needed, they undergo apoptosis. The function ofeffector cells is to remove the stimulus that activated them, butwhen that stimulus is gone, the effector cells no longer haveanything to remove except for themselves, which occurs throughapoptosis. Apoptosis causes cells to die, and they are subsequentlyremoved through macrophages. They are capable of identifying thedying cells through the composition of their membrane, specificallythe lipid phosphatidylserine. In a normal cell, the lipid is foundon the inner portion of the plasma membrane. However, when a cellundergoes apoptosis, it redistributes to the outer surface whichallows for easy recognition by phagocytes. While some effectorcells are removed, some are retained to allow for formation ofmemory T-cell and B-cells (1). The acquired protective immuneresponse is critical in providing protection against pathogens. Itis acquired through effector T cells or antibodies that aregenerated when exposed to the pathogen, as described above. Thiscan be done by initial infection or through vaccination that allowsfor immunological memory. The specific pathogen involved influencesthe type of effector T cell or antibody that provides protection.For example, the polio inactivated vaccine utilizes preexistingantibodies (IgA) to neutralize the virus and prevent its spread ofinfection (1). These antibodies are known as IgA, and are producedwithin the gut mucosa. In order to activate the mucosal immuneresponse, antigens are transported across the epithelium throughthe use of microfold (M cells). They are then presented to effectorB lymphocytes that result in stimulated B cells to migrate todistant mucosal cites. This ultimately leads to the production ofIgA that neutralizes the antigen. The neutralization of thesesubstances prevents it from binding to receptors within the tissue.Therefore, the neutralized antibody-antigen complex formed isultimately removed and destroyed by macrophages (2).
