Antigen-presenting cells (APC) of mice with chronic graft-versus-host disease (GVHD) cause excessive activation-induced death of T helper cells.

Abstract

Both experimental and clinical forms of chronic GVHD have unique immunological features. The affected animals/individuals suffer from autoimmune disorders such as systemic lupus erythematosus (SLE), and yet they are unable to mount a self MHC-restricted T cell response to foreign antigens. Pathogenesis of the latter phenomenon was investigated in an experimental model of chronic GVHD. Chronic GVHD was induced in 8-10-week-old (B6xC3H)F1 mice by tail vein injection of 5 x 10(7) spleen cells of C3H parental strain. The recipients, when tested 3 months later, were unable to mount a T helper (Th) cell response to a randomly selected immunogen, a vaccine of l0(8) killed Mycobacterium vaccae. The animals showed evidence of generalized lymphoid hyperplasia, as indicated by GVH index >1.34, and also revealed autoantibodies against erythrocytes and dsDNA, indicating establishment of chronic GVHD. However, mice with chronic GVHD of only 3 weeks duration were able to mount the Th cell response to M. vaccae. Three consecutive immunizations of these mice at 1-week intervals, with the same immunogen, resulted in the mice becoming non-responsive to the antigen. All the three responses tested, namely the DTH, lymphoproliferation and the antibody responses, were adversely affected. The non-responsiveness induced was antigen-specific. Mice receiving two immunizations with M. vaccae responded normally to Salmonella enteritidis. Pulse treatment with cyclosporin A 0.5 mg/mouse by the i.p. route, on days 0, 1, 2, 3 and 4 at the time of immunization with M. vaccae on day 1, prevented emergence of non-responsiveness. Based on this evidence, it was concluded that repeated activation of T cells of mice with chronic GVHD induces non-responsiveness. Extent of clonal loss due to activation-induced cell death (AICD) caused by i.p. injection with a superantigen Staphylococcal enterotoxin B (SEB) was investigated in F1 mice with chronic GVHD. I.p. injection of 25 microg/mouse of SEB induced loss of SEB responding clones in both normal F1 mice and those having chronic GVHD; however, the extent of loss was much greater in the latter. In vitro antigen-specific proliferation of primed splenic T cells of normal F1 mice was observed to be quite poor when antigen was presented by APC of mice with chronic GVHD of 3 weeks duration. Proliferation profiles of T cells of normal F1 mice, in response to stimulation with concanavalin A (Con A) or SEB, were studied, using as APC irradiated spleen cells of normal F1 mice or of F1 mice with chronic GVHD of 3 weeks duration. With Con A and APC of normal F1 mice, peak proliferation was observed at 48 h, which remained at the same level up to 72 h and declined thereafter, possibly due to AICD. With SEB and the normal APC, proliferation progressively peaked at 72 h and declined thereafter. With APC of mice with chronic GVHD, the 48 h proliferative responses of both Con A and SEB were comparable to those caused by APC of normal F1 mice; however, thereafter the responses declined steeply, suggesting greater AICD. Based on these results, it was concluded that APC of mice with chronic GVHD are functionally altered to induce greater AICD.