Immune response lymphoid organs

The cells involved in the immune responses are organized into tissues and organs in order to perform their functions most effectively. These structures are collectively referred to as the lymphoid system, and are arranged into either discretely encapsulated organs or accumulations of diffuse lymphoid tissue. The major lymphoid organs and tissues are classified as either primary (central) or secondary (peripheral). Lymphocytes are produced in the primary lymphoid organs and function within the secondary lymphoid organs and tissues. 

After activation, cytotoxic T cells emerge from lymphoid organs to infiltrate the graft and trigger the immune response. These cells have been shown to induce graft destruction via two mechanisms (1) secretion of the cytotoxic proteins perforin and granzyme B, and (2) induction of cellular apoptosis... 

Forster R, Schubel A, Breitfeld D, et al. CCR7 coordinates the primary immune response by establishing functional microenvironments in secondary lymphoid organs. Cell 1999 99 23-33. 

Immunotoxicity. There are currently no data on the effects of 2-hexanone on the human immune system via any route of exposure. Animal data included an inhalation study in which there was a 40% decrease in peripheral white blood cells in rats exposed to 2-hexanone (Katz et al. 1980). In addition, 2,5-hexanedione, a metabolite of 2-hexanone, was shown to adversely affect lymphoid organs of the immune system in rats and to cause impairment of immunity in mice (Upreti and Shanker 1987). Immunological assessments, including analysis of peripheral blood components and effects on lymphoid tissue, conducted as part of intermediate-or chronic-duration studies and skin sensitization tests would be useful in developing a dose-response relationship and assessing the potential risk to chronically exposed persons in the vicinity of hazardous waste sites or to exposed workers. 

The materials capable of stimulating the lymphoid tissues to produce antibodies are termed antigens and comprise bacterial and viruses as well as some smaller molecular entities. However, the response is not to the intact organisms but rather to some specific parts which have characteristic three-dimensional structures, the epitopes, and this sensitivity to structure is a characteristic feature of the immune response. Once an animal is in contact with an epitope the response can be in the circulatory or humoral system or directly as a cell-mediated response, but it is exquisitely sensitive to the specific antigen and rarely to any other. 

Thus, human exposure to PCBs in Japan (Yusho accident) and China has been associated with increased respiratory infections and decreased levels of immunoglobulins in serum. In animals exposed to these compounds, there is atrophy of both primary and secondary lymphoid organs, lower circulating immunoglobulins, and decreased antibody responses after exposure to antigens. Similarly, the exposure of both humans and farm animals to polybrominated biphenyls, which occurred in Michigan in 1973, resulted in depressed immune responses. 

Two different classes of white cells, or lymphocytes are associated with the immune response The B cells and the T cells. In mammals, B lymphocytes mature in the bone marrow and then migrate to secondary lymphoid organs... 

In addition to causing lymphoid organ weight changes, 2,3,7,8-TCDD has been shown to cause functional alterations in the immune response (Vecchi et al. 1980a). Studies have shown that suppressed... 

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