In vivo and in vitro repertoire of CD3+CD4 CD8 thymocytes

CD4-CD8- thymocytes contain a cell subset which expresses thecomplete CD3-TCR complex (/ or /) of which the ontogeny andfiliation are unknown. One of the questions is whether thispopulation can be intrathymically selected, an obligatory stepfor the mature CD4⁺ and CD8⁺ cell differentiation pathway, orif the absence of CD4 and CD8 allows them to escape thymic selection.The repertoire of CD3 ⁺ CD4 - CD8 - (CD3 ⁺ DN) thymocytes wasanalyzed in different strains of mice with different combinationsof H-2 and Mls expression. The expression of V_ß8.1in freshly isolated CD3⁺ DN cells is the highest in Mls-l^b miceand the lowest in MIS-l^a and F₁ mice, suggesting that selectionagainst this specificity can be achieved in vivo. By contrast,a low percentage of V_ß6⁺ cells is found in all thestrains, with no correlation according to MIS expression. Invitro culture of DN thymocytes with IL-1 and IL-2 leads to theproliferation of CD3⁺ DN cells. In vitro culture amplifies thein vivo pattern of V_ß8.1 expression, while V_ß6⁺cells only expand in DN cells of 66 and 61002 Mls-l^b mice withthe same genetic background. These results show: (i) CD3⁺ DNthymic cells can be intrathymically selected but the repertoireis different from that of mature T cells; (ii) V_ß6and V_ß8.1 selection do not follow the same pattern;(iii) this repertoire can be modified by In vitro culture, towarda more mature type; and (iv) comparison of DN cell repertoireof BALBlc, BALB.D2 (congenic for MLs), and other strains ofmice suggests a multigenic control for this selection, and aninvolvement of background genes.