Cellular components of the immune system

T-Lymphocytes (4,5) and other cellular components of the immune system also have equally wide implications in regulation of the normal immune system. The T-lymphocytes play a central role in the body s response to harmful antigens and tumor—host interaction (4). Responses involve antigens derived from vimses, bacteria, parasites, and tumors. T-ceUs also participate in the immune surveillance response, where self-antigens are recognized, but usually sequestered within the cell and, when exposed, become markers of cellular damage. 

Psychological stress may influence the immune system by activation of the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic-adrenal-medullary axis (SAM). The well-described innervation of primary and secondary lymphoid tissues by the autonomic nervous system also has been implicated in stress-related modulation of the immune response. These pathways operate by producing biological mediators that interact with and affect cellular components of the immune system.13... 

TABLE 15.4. Cellular Components of the Immune System and Their Functions... 

Passive immunization consists of transfer of immunity to a host using preformed immunologic products. From a practical standpoint, only immunoglobulins have been used for passive immunization, since passive administration of cellular components of the immune system has been technically difficult and associated with graft-versus-host reactions. Products of the cellular immune system (eg, interferons) have also been used in the therapy of a wide variety of hematologic and infectious diseases (see Chapter 56). 

Terms - There are specific terms used for the biochemical and cellular components of the immune system. The following are the key ones to remember. 

Opioid receptors are present in human T-cell lymphocytes (Wybran et al., 1979), which may provide a link between the central nervous system and the immune system. There is a considerable body of literature, which demonstrates a modulatory function of the immune system by opioids. Opioids alter the biochemical and proliferative properties of various cellular components of the immune system (Webster, 1998). (3-Casomorphins affect the human mucosal immune system, possibly via the opiate receptor, since the opiate receptor antagonist, naloxone, reverses the activity (Elitsur et al., 1991). P-Casomorphins and a-casein exorphins inhibit the cell proliferation of human prostate cell lines by a mechanism partly involving opioid receptors (Kampa et al., 1997). 

The most obvious example of a cellular component of the immune system is the lymphocyte and includes all the various subtypes of T and B cells. As indicated previously, the fundamental distinction between T cells and B cells is based on the specific primary lymphoid organ in which the final stages of lymphopoiesis takes place. As described below, these cell types can also be distinguished based on their respective functions within the immune system as well as by phenotypic characteristics. For the purposes of this entry, a phenotype will be defined as a marker expressed on the surface of a cell which is genetically determined and which is frequently associated with the specific function of that... 

The basis for the effector function by antigen-specific lymphocytes - especially antibody-secreting B cells, Td cells, and Tc cells - and the participation of other cellular components of the immune system in acquired immunity - including NK cells, macrophages, and neutrophils - have already been emphasized in other sections of this volume. It has also been emphasized that Th cells play an important effector role in acquired immunity as regulators in the growth and differentiation of B cells and Tc cells. In this regard, it is important to note that both populations of T cells whose participation in an acquired immune response is mediated by the secretion of lymph-okines, that is, Th and Tq cells, are characterized by the expression of CD4. 

Alcoholics are more prone to infections, such as TB and pneumonia, than non-alcoholics. Many of the cellular components of the immune system, such as T cells and natural killer cells which are involved in immune surveillance, are reduced in number and responsiveness. This causes the immune system to be compromised in alcoholism, and cancer surveillance is thereby also reduced. 

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