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Immunization of single lymph nodes with various antigens led to the appearance of cells in the efferent lymph that secreted antibody specific for the antigen which induced their formation and for a number of unrelated, non-crossreacting anti-gens. Immunization of single lymph nodes with mitogens led to the appearance of cells secreting antibodies specific for an even greater number of antigens, including one (TNP) that in all probability is not present in the animals' natural environment. When the node was primed with one antigen, a subsequent challenge with an unrelated antigen 12 weeks later led to the appearance of greater numbers of cells containing and secreting antibody against the previously experienced antigen, than was the case in unprimed lymph nodes. These findings indicate that the immune response to antigen provokes the maturation of lymphocytes of specificities unrelated to that of the injected immunogen. Such a mechanism may be important in maintaining immunological memory. Mitogens may directly activate lymphocytes into maturation and expression as antibody-secreting cells, whereas antigens appear to act indirectly. [ABSTRACT FROM AUTHOR]

Tissue-specific circulation of T cells is a critical element in the integration of systemic immune responses. Current models of T-cell migration suggest that homing specificities oft cells for tissues such as gut and skin are generated outside the thymus as a result of activation of virgin T cells by antigen in lymph nodes. We have used the sheep fetus (which is immunologically virgin and contains no memory or effector T-cell subsets) to examine the migration of 51Crk-labelled T cells in vivo. We report that gut-homing T cells are not present in the fetus and that gut-homing T cells from postnatal lambs home normally to fetal gut. Fetal thymectomy performed immediately prior to birth failed to prevent the development of gut-homing T cells in postnatal life. Gut-homing specificities on T cells are thus acquired extrathymically. [ABSTRACT FROM AUTHOR]

Two mouse monoclonal cytotoxic antibodies (ST-Ia and ST-Ib) recognize an antigen present on the large majority of thymocytcs and all T cells in the periphery. but not B cells or other haemopoietic cells in sheep. Examination of frozen sections of various fetal tissues revealed that the cells expressing this antigen first appeared in the thymus, and these cells markedly increase in numbers in the peripheral lymphoid tissues after mid-gestation. Large accumulations of positive cells were located in the paracortex of lymph nodes, the periarteriolar lymphoid sheath of the spleen, and interfollicular areas of jejunal Peyer's patches. all of which are known to be T-dependent areas. Treatment of lymphocytes with ST-Ia and complement resulted in the abrogation of T-proliferative responses, but the response to a B-cell mitogen. lipopolysaccharidc. was not reduced. Neither ST-Ia, nor ST-Ib cross-reacted to lymphocytes obtained from other species of animals (man, monkey, mouse, rat, guinea. pig, chicken, frog, pig, horse, goat and cattle). Based on these findings, it was concluded that the expression of the antigen recognized by ST-Ia and ST-Ib is restricted to the T-cell lineage of sheep, and that all ovine I cells express this antigen. Furthermore, ST-Ia and ST-Ib were determined to recognize the same antigen by reciprocal blocking experiments. [ABSTRACT FROM AUTHOR]

The ileal Peyer's patches (IPP) of sheep may be a primary lymphoid organ for B cells since they have a number of important features in common with the bursa of Fabricius of chickens. We have examined the surface phenotype of IPP cells. Approximately 90% to 95% of IPP cells are ‘low sIgM+’; that is, they have surface IgM, but in much smaller amounts than peripheral B cells, which arc ‘high sIgM+’. I PP cells with sIgG or alga are very rare. Upon exposure to a tumour promotor, phorbol myristate acetate (PMA), in vitro, low sIgM+ cells differentiated into high sIgM+cells. The amount of Ia-like antigens on the surface also increased after PMA treatment. Approximately 5% of IPP cells bore no identifiable markers. However, these cells could also be induced into high sIgM+ cells upon exposure to PMA; this may indicate the presence of precursors of sIgM+ cells within the IPP. While PNA (peanut agglutinin) binds strongly to the vast majority of IPP cells, it binds very little, if at all, to B cells obtained from the periphery, unless they have been treated with neuraminidase; this suggests that cells in the B lineage retain their PNA receptors, but that these become masked by sialic acid on mature B cells. [ABSTRACT FROM AUTHOR]

The results presented in this paper demonstrate that a mouse IgM monoclonal antibody (T-80) recognizes an antigen on cells of the T-lymphocyte lineage of sheep. However, this antibody does not identify all T cells, as 10-20% of thymocytes and some peripheral-blood T cells are negative. T-80- thymocytes reside in the medulla. The majority of cortical thymocytes are T-80+ and classified as dull cells on the basis of antigen density per cell as measured by flow microfluorometry. In contrast, T-80+ cells in the periphery can be categorized into two populations, i.e., dull cells and bright cells. Suggestive evidence was obtained that bright T-80+ cells are fast recirculating T cells, whereas dull ceils are sessile or less easily mobilizable T cells in the periphery. In foetal environment, over 90% of thymocytes and approximately 5% of spleen cells are T-80+ at 54 days of gestation (gestation period = 150 days), which may indicate that T-cell emigration from the thymus commences well before mid-gestation in sheep. [ABSTRACT FROM AUTHOR]

T lymphocytes derived from different sources in sheep were compared for their ability to recirculate from blood to lymph. Nylon wool columns were used to prepare T-cell-enriched populations from efferent intestinal lymph, efferent prescapular lymph and from cell suspensions of mesenteric lymph nodes and prescapular lymph nodes. With each animal, T cells from two of the above sources were labelled in vitro, one population with fluorescein isothiocyanate the other with rhodamine isothiocyanate; both populations were returned to the animal at the same time by intravenous injection. The intestinal lymph and prescapular lymph were continuously monitored to compare the recirculating properties of the two populations oft cells. This technique led to confirmation of the earlier reports in sheep ora preferential recovery of intestinal lymph T cells and of prescapular lymph T cells in the lymph from which the cells were originally collected. This phenomenon was much less evident with T ceils from mesenteric nodes and prescapular nodes and in a number of experiments a random pattern of recirculation occurred. It is concluded that there are differences in the composition of the T-cell population in a node compared with that of the lymph draining the node. The advantages of using fluorescently-labelled cells to study lymphocyte migration are discussed. [ABSTRACT FROM AUTHOR]