Acquired cell-mediated immunity

Anthony LSD, Kongshavn PAL. H-2 restriction in acquired cell-mediated immunity to infection with Francisella tularensis LVS. Infect Immun. 1988 56 452-456. 

Immune systems in animals and plants are quite different. There are two types of immune systems in animals (1) innate, so-called non-specific or passive immunity (2) adaptive, so-called specifically acquired , active, or cell-mediated immunity. Innate immunity is based on barriers to infectious agents and adaptive immunity is based on multiplicative and specific antibody release after contact with an antigen (infectious agent). The so-called memory cells in animals respond to secondary contact with an antigen. 

Bui, T., T. Dykers, S.L. Hu, C.R. Faltynek, and R.J. Ho, Effect of MTP-PE liposomes and interleukin-7 on induction of antibody and cell-mediated immune responses to a recombinant HIV-envelope protein. J Acquir Immune Defic Syndr, 1994. 7(8) 799-806. 

Glucocorticoids inhibit acquired or cell-mediated immunity. Their effects are mediated via inhibition of genes that code for various cytokines. The cytokines inhibited by glucocorticoids include IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, IL-8 and IFN-y. IL-2 inhibition by corticosteroids is the most crucial effect in immunosuppression, which results in the inhibition of T-cell proliferation and activation of cytolytic T cells. Glucocorticoids also slightly affect humoral immunity by inhibiting B-cell clonal expansion and antibody synthesis, and these effects are mediated via their ability to inhibit B cells ability to express IL-2 and IL-2 receptors. 

Acquired immunity is antigen dependent and comprises all the specific immunological reactions associated with lymphocytes. In light of the existence of an antigen-specific defense system, a legitimate question arises as to why we have such an elaborate nonspecific immune system. One of the primary reasons may be that an acquired immune response takes time. For example, 5 days are needed to generate a primary antibody response, and the body must rely on the innate immune system to hold the infection in check during this time. As noted previously, acquired immunity can be subdivided into two effector arms, humoral immunity and cell-mediated immunity. The humor (i.e., a bodily fluid) associated with humoral immunity is the secreted form of Ig in the blood. The cells associated with cell-mediated immunity are the various subpopulations of T cells. 

All three of these mechanisms will be highlighted in the discussion of the five basic steps of an acquired immune response, which are illustrated below and which are depicted in Figure 2 for the generation of an antibody response. It is important to emphasize that these same five steps are involved in the generation of a cell-mediated immune response ... 

Cell-mediated immunity (CMI), often referred to as T cell-mediated immunity, refers broadly to any host resistance mechanism in which cellular elements play a direct role and which is part of the acquired arm of immunity. This is in comparison to humoral immunity, in which there are certainly cellular interactions but the final host resistance products are soluble factors such as... 

The acquired immunodeficiency syndrome (AIDS) is a condition characterized by the development of life-threatening opportunistic infection or malignancies with severe depression of the T-cell mediated immune system caused by infection with human immunodeficiency virus (HIV). 

AIDS (acquired immune deficiency syndrome) A disease of humans characterized by defective cell-mediated immunity and increased snsceptibilltyto infections. It is caused by the retrovims HIV (human immunodeficiency vims). This infects and destroys helper "T cells, which are essential for combating infections. HIV is transmitted in blood, semen, and vajpnal fiuld the major rontes of infection are unprotected vajpnal and anal intercourse, intravenous drug abuse, and the administration of contaminated blood and blood prodncts. A person infected with HIV is described as HIV-posldve after the initial infection the vims can remain dormant for np to ten years before AIDS develops. Antiviral dmgs can delay the development of fiiU-blown AIDS, in some cases for many years. 

The theoretieal baekground whieh underlies immunity to infection has been discussed in detail in Chapter 14. Immunity to infeetion may be passively acquired through the receipt of preformed, proteetive antibodies or it may be aetively acquired through an immune response following deliberate or accidental exposure to microorganisms or their eomponent parts. Aetive aequired immunity might involve either or both humoral and cell-mediated responses. 

Acquired immunity is immunity that develops with exposme to antigens the immune system builds a defence that is specific to that antigen. B-ceU lymphocytes, produced in the stem cells of the bone marrow, synthesise and release antibody they oversee the humoral immune response. T-ceU lymphocytes, produced in the bone marrow but sensitised in the thymus, are the basis of the ceU-mediated immune response. 

As stated above, the principal objective for the use of an adjuvant in a vaccine is to potentiate immune response to an Ag of minimal immunogenicity. How this potentiation is achieved varies from adjuvant to adjuvant and in many cases, the precise mechanism of ac tion is unknov n. However, as a rule, immune potentiation is accomplished by the ability of the adjuvant to induce a variety of non-specific activities within the innate arm of the immune system. Once activated, the innate branch of immunity, particularly the complement system, orchestrates the various humoral and cell-mediated responses that operate within and between the innate and acquired arms. The result is a generalized activation and potentiation of the immune system in response to the adjuvant with the hope that this generalized immune priming will allow for a more effective processing and recognition of the Ag contained within the vaccine. 

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