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The avian primary lymphoid organs, the bursa of Fabricius and the thymus, are crucial to the normal development of B and T lymphocytes in birds. Birds use gene conversion to produce different classes of immunoglobulins and this process occurs in the bursa of the Fabricius. The microenvironment of the bursa selectively expands those B-cell precursors that have undergone productive V(D)J recombination. On the other hand, the thymus constitutes the microenvironment for T lymphocyte differentiation and the acquisition of self-tolerance. Production of T cells in the thymus is controlled by a combination of positive and negative selection. The differentiation of T cells proceeds along two pathways characterized by the expression of αβ or γδTCRs. Immunologically mature lymphocytes enter the circulation and colonize the peripheral lymphoid organs.
The structure and function of the immune system of pigs are the main subjects of interest to numerous research centers, which is undoubtedly related to the potential of using pig organs in xenotransplantation. Another reason for intensive studies on this subject is the need for secure and effective immunoprophylaxis of pigs and the improvement of their immunological status. The present paper presents the current knowledge on the prenatal ontogeny of lymphocytes in pigs. The ontogeny of pigs’ immune system starts in early gestation. During the prenatal period the system undergoes numerous changes which ultimately result in its achievement of immunological competence. Although the immune system in pigs is physiologically developed already on the 35th day of pregnancy, only a small numbers of lymphocytes and other lymphatic elements can be detected in fetal organs. The hematopoiesis in bone morrow starts around the 45th day of pregnancy. Lymph nodes, including mesenteric lymph nodes, are devoid of their defense function until the 70th day of prenatal life. The most dynamic development of the immune system of pigs takes place between the 60th and 90th day of gestation. To a greater extent, the diffusion of lymphocytes in secondary lymphatic organs occurs after birth, and the intensity of this process seems to be related to the colonization of the gut and enhanced by the contact of newborns with environmental antigens.
The aim of the study was to show the dynamics of lymphocytes T (receptor CD5+ ), Th (receptor CD4+), Tc/Ts (receptor CD8+), B (receptor IgM . mu chain), as well as lymphocytes with receptor CD25+ in rabbits immunised with Chlamydophila abortus and Chlamydophila psittaci. Moreover, a serological test was carried out. The analysis of the results indicated that the immunisation of rabbits with the studied antigens in case of lymphocytes T and their subpopulations caused a similar increase and decrease of their amount and in case of lymphocytes B only an increase. Those changes are noted in 7th . 14th day after the immunisation and they persist until 42nd . 56th day of the experiment. Moreover, the positive titre of antibodies was noticed on the 35th . 42nd day after the immunisation, i.e. 4-6 weeks after the changes in the amount of lymphocytes.
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