In Vivo homeostatic proliferation of purified CD4+ T cells, but not purified CD8+ T cells, is decreased early after burn injury

Abstract

Introduction: Homeostatic proliferation (HP) is increasingly recognized as essential for a prolonged, antigen-independent, adaptive immune response to insults such as injury or inflammation. While severe burn injury results in persistent and substantial immune dysfunction, the effect of burn injury on HP remains unclear. In this study, we investigated the effect of burn injury on the in vivo homeostatic proliferation of purified CD4+ and CD8+ T cell subsets following irradiation and adoptive transfer. Methods: C57BL/6 female mice received 6 Gy (600 rads) of ionizing radiation and 48 hours later, either whole splenocytes (WS), or purified CD4+ T cells, or CD8+ T cells, all labeled with CFSE, were adoptively transferred via intraperitoneal injection. After an additional 48 hours, mice received a 20% contact burn or sham injury. An additional 72 hours later, (3 days post burn, 5 days post transfer, and 7 days post irradiation) mice were sacrificed and splenocyte proliferation was analyzed by flow cytometry. Proliferation was determined as percent CFSE+ cells having undergone at least one cell division and data were analyzed using Student’s t-test with significance defined as p < 0.05. Results: Purified CD4+ T cell HP (56.35%) was greater than whole spleen (WS) CD4+ T cell HP (38.34%) in sham mice. Burn injury however dramatically decreased purified CD4+ T cell HP (14.60%) compared to WS CD4+ T cell HP in burn (32.05%, p < 0.05), WS CD4+ T cell HP in sham (38.34%, p < 0.05), and purified CD4+ T cell HP in sham (56.35%, p < 0.05). This effect was not observed with purified CD8+ T cells, where purified CD8+ T cell HP (45.62%) in burn was not impaired compared to CD8+ T cell HP in sham (38.55%). Conclusion: This study demonstrates that burn selectively and dramatically impairs the homeostatic proliferation of adoptively transferred purified CD4+ T cells. This study emphasizes the differential effect of burn injury on CD4+ and CD8+ T cells and suggests that a possible mechanism may be a specific, deleterious effect of burn injury on CD4+ T cells and/or a unique beneficial effect of CD8+ T cells or other cells on HP after burn injury.