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One of the key synchronizers of mammalian circadian rhythm is the hormone melatonin (MT) produced by the pineal gland. MT is characterized by a wide spectrum of biological activity including its immunopotentiating effect. At the same time, the results of studies dedicated to the effects and mechanisms of melatonin immunoactivity seem to be contradictory. Studies conducted by the authors of this article show that diurnal variations in MT content in blood and saliva of healthy humans demonstrate significant individual fluctuations connected with the seasonal factor. The character of MT relations with the immune system varies depending on the phase of the circadian cycle. Patients with immunopathological condition (bronchial asthma--BA) demonstrate a reduced number of correlations between MT level and immunological parameters. After treatment, the positive dynamics of immunological and clinical parameters in BA patients is associated with an increased number of correlations between the immunological status parameters and MT level in blood, which may indicate an increase in its immunoregulatory role. Administration of melatonin and amitriptyline, the inductor of its synthesis, in animals kept under continuous light helped to recover normal circadian rhythmicity in the cell content of lymphoid organs. Solving problems associated with the immunomodulating and synchronizing role of MT could give researchers an insight into the details of neuroendocrine and immune interrelations and help to develop new methods for the prevention and correction of immune status disturbances in diseases and desynchronoses (stresses, jet lags, shift and night work, etc.).

The biological rhythmological programme of the immune system is a constituent of the body's common biological rhythmological programme. Its pattern seems to be genetically determined and reflects the functional status of the system. The chronobiological mechanisms responsible for the regulation of immune functions lie in the presence of certain phasic interrelations between the biological rhythms of the synthesis and production of regulatory agents on the one hand, and those of the receptor system and metabolic potential of immunocompetent cells on the other. The facts given in the paper may be a basis for a chronobiological approach to better understanding the mechanisms of the physiology and pathology of the immune system. The medical significance of study of the structural and temporal pattern of the immune system consists in the development of new techniques for diagnosis, prognosis, therapy, and assessment of risk factors in immunopathological conditions.

The paper discusses what immunomorphology is, which place it occupies in immunology today after methods of molecular biology, gene engineering, biotechnology have been intensively used in research, what basic methods and approaches are applied to immunological studies. Data available in the literature on the development, establishment, and prospects of immunomorphology and some morphofunctional evidences obtained by the Laboratory of Immunomorphology, Institute of Clinical and Experimental Morphology. Siberian Branch of the Russian Academy of Medical Sciences, from the physiological and morphocytochemical studies of the lymphoid system in health and in disease with circadian variations in mind.

The paper provides the results of examining about 3,000 industrial workers exposed to various xenobiotics. Various phases of immune responses were noted in 40-60% of persons with nonspecific chronic pulmonary, gastrointestinal, gynecological diseases at remission. 10-20% of the industrial workers under study were diagnosed as having secondary immunodeficiency whose criteria were the presence of one of clinical syndromes, a sharply significant reduction in immunoglobulins, normal levels of circulating immune complexes and normal values of the lymphocytic enzymes alpha-glycerophosphate dehydrogenase, succinate dehydrogenase, lactate dehydrogenase. The stimulation of the immune system in clinically healthy individuals who have a service length of 3 year or more should be regarded as development of an immune response to a xenobiotic or its metabolites.

The paper provides the authors' own data and the data available in the literature concerning diurnal rhythms of immunological parameters in the development of experimental immunopathological conditions. Desynchronizing these rhythms, a change in the light regime is shown to accelerate the time course of the development of an autoimmune process in mice. The potentialities of chronotherapy of experimental immunodeficiencies with thymic preparations have been studied. It is emphasized that chronobiological studies are particularly essential in solving the biomedical problems of the Far North with its extreme conditions and a great deal of desynchronizing factors.