Peripheral T cell survival requires continual ligation of the T cell receptor to major histocompatibility complex-encoded molecules

Abstract

In the thymus, T cells are selected according to their T cell receptor (TCR) specificity. After positive selection, mature cells are exported from primary lymphoid organs to seed the secondary lymphoid tissue. An important question is whether survival of mature T cells is an intrinsic property or requires continuous survival signals, i.e., engagement of the TCR by major histocompatibility complex (MHC) molecules in the periphery, perhaps in a similar way as occurring during thymic positive selection. To address this issue we used recombination-activating gene (Rag)-deficient H-2b mice expressing a transgenic TCR restricted by I-Ed class II MHC molecules. After engraftment with Rag-/- H-2d fetal thymi, CD4+8- peripheral T cells emerged. These cells were isolated and transferred into immunodeficient hosts of H-2b or H-2d haplotype, some of the latter being common cytokine receptor gamma chain deficient to exclude rejection of H-2b donor cells by host natural killer cells. Our results show that in the absence, but not in the presence, of selecting MHC molecules, peripheral mature T cells are short lived and disappear within 7 wk, indicating that continuous contact of the TCR with selecting MHC molecules is required for survival of T cells.

Figure 1

Thymic development of CD4⁺8⁻ T cells in H-2^d fetal thymus–grafted H-2^b ABII TCR Rag^−/− mice. H-2^b ABII TCR Rag^−/− mice were transplanted with BALB/c fetal thymi that had been treated with dGuo. Several weeks after transplantation, thymocytes from grafted and host thymi were recovered and analyzed by four-color flow cytometry including the ABII TCR–specific mAb 6.5. Similar data were obtained when grafting H-2^d Rag^−/− thymi that, however, grew much more extensively (average of 3.5 × 10⁷ thymocytes).

Figure 2

CD4⁺8⁻ lymphocytes are present in H-2^b ABII TCR Rag^−/− mice grafted with an H-2^d fetal thymus. Lymphocytes were recovered from H-2^d ABII TCR Rag^−/− and H-2^b ABII TCR Rag^−/− mice that had previously been transplanted with fetal thymus lobes from H-2^d Rag^−/− mice. Cells were analyzed by four-color flow cytometry as shown.

Figure 3

CD4⁺8⁻ lymphocytes from H-2^d thymus-grafted H-2^b ABII TCR Rag^−/− mice disappear in H-2^b adoptive hosts. 7.5 × 10⁵ CD4⁺8⁻ and 5 × 10⁵ CD4⁻8^low lymphocytes from H-2^d Rag^−/− fetal thymus–transplanted H-2^b ABII TCR Rag^−/− mice were adoptively transferred into H-2^b and H-2^d nu/nu mice. 7 wk later, cells from lymph nodes and spleen (RBCs lysed) were isolated, depleted of sIg⁺ cells, and analyzed by four-color flow cytometry. Data from lymph nodes and spleen gave similar results. Calculated numbers of 6.5⁺HSA⁻ cells were 5,600, 6,500, and 1,800 for CD4⁺8⁻ and 1,800, 463,600, and 400 for CD4⁻8^low cells in unmanipulated H-2^b (one mouse), injected H-2^b (average of two mice), and injected H-2^d (average of two mice) nu/nu mice, respectively. (Note that numbers also contain the calculated background values of mice not injected.) Another experiment and two experiments using H-2^b Rag^−/− and H-2^d Rag^−/− recipients gave similar results.

Figure 4

CD4⁺8⁻ lymphocytes from H-2^d thymus-grafted H-2^b ABII TCR Rag^−/− mice survive in H-2^d NK cell–deficient adoptive hosts. 10⁵ CD4⁺8⁻ and 10⁵ CD4⁻8^low lymphocytes from H-2^d Rag^−/− fetal thymus–transplanted H-2^b ABII TCR Rag^−/− mice were adoptively transferred into H-2^b Rag^−/− and H-2^d Rag^−/− IL-2Rγ^−/− mice. 7 wk after transfer, cells from lymph nodes and spleen were analyzed as in Fig. 3. Calculated numbers of 6.5⁺HSA⁻ cells were 900, 13,500, 5,900, and 3 × 10⁶ for CD4⁺8⁻ and 600, 6,100, 7.6 × 10⁵, and 1.5 × 10⁶ for CD4⁻8^low cells in unmanipulated H-2^d Rag^−/− IL-2Rγ^−/−, unmanipulated H-2^b Rag^−/− (not shown), injected H-2^b Rag^−/−, and injected H-2^d Rag^−/− IL-2Rγ^−/− mice, respectively. Expansion in Rag-deficient H-2^d mice was consistent with previous data (41). We also performed this type of experiment with two thymectomized H-2^d Rag^−/− IL-2Rγ^−/− mice and obtained similar results.