Selective suppression of granuloma formation and delayed hypersensitivity in rabbits

Immunology of sarcoidosis

Because of its association with cutaneous anergy, sarcoidosis was originally viewed as a defect of cellular immunity. Supporting that misperception were early studies of peripheral blood lymphocytes that found lymphopenia and impaired lymphocyte responses to mitogens and recall antigens. The clue to a vast underlying network of complex hyperactive cellular immune functions was discovered in the paradoxical finding of in vitro spontaneous lymphoblastic transformation and lymphokine production. Subsequently, investigative focus shifted to the activated, proliferating T-helper lymphocytes, the lymphokines of which were found to function in the recruitment and retention of monocytes for granuloma development. T-helper lymphocytes also contributed to the mechanism of hypergammaglobulinemia through their influence on B cells. The most intriguing question about sarcoid immunology is the initiating factor that triggers the T-lymphocyte activation and proliferation in the first place. There is much to suggest that antigen processing and presentation launches the process. Because lymphocyte activation and proliferation antedate granuloma formation at K-S skin test sites and in the lung, we combined the harvesting technique of BAL with the K-S bioassay to show that granulomagenic antigen is being processed by monocyte-macrophages. The finding of autologous monocyte-macrophage granulomagenicity raises the distinct possibility that sarcoidosis is a unique cell-mediated type of autoimmune process. The isolation and identification of the granulomagenic factor is the exciting research frontier ahead.

Increased hyaluronic acid is associated with dermal delayed-type hypersensitivity

Rabbits sensitized subcutaneously with heat-killed bacilli Calmette-Guerin (BCG) and challenged intradermally with heat-killed BCG or purified protein derivative (PPD) demonstrated classical dermal delayed-type hypersensitivity which peaked two days postchallenge. Animals challenged with BCG developed dermal granulomas as measured by induration and gross observation. Challenge with either PPD or BCG resulted in increased levels of dermal hyaluronic acid (HA) by two days postchallenge. Dermal HA returned to normal levels by seven days postchallenge regardless of the challenge antigen. These results indicated that increased HA is associated with dermal delayed-type sensitivity, but increased HA is not associated with dermal granulomatous hypersensitivity. These results are in contrast to previously reported work which indicates that increased HA is associated with both pulmonary delayed hypersensitivity and pulmonary granulomatous hypersensitivity.

Diseases associated with immunosuppression

Impairment of any of the major components of the immune system (T-cells, B-cells phagocytes, complement) may result in clinical immunodeficiency. Immune defects can arise from intrinsic or heritable defects of lymphoid elements, failure of normal cellular differentiation, viral infection or other acquired causes. Clinical impairment of immunity is expressed as a marked susceptibility to opportunistic and pathogenic organisms which are difficult to control and by an increased risk of malignancy, allergy and autoimmune disease. Certain immunodeficiency disorders are associated with aberrant immune regulation. The major types of immune deficiency are characterized by unique patterns of infections depending on the level at which the defect occurs and the pathogenic mechanisms of the parasite. The basic defects of representative primary and secondary immunodeficiencies are discussed in relation to observed immunologic consequences.