A dominant role for non-MHC gene effects in susceptibility to cyclosporin A (CsA)-induced autoimmunity

Abstract

Lethally irradiated LEW rats reconstituted with syngeneic bone marrow and given CsA for a 4-week period develop a graft-versus-host-like disease upon withdrawal of CsA. This T cell-mediated autoimmune disease is referred to as CsA-induced autoimmunity (CsA-AI). CsA-AI-susceptible LEW rats and resistant BN rats differ greatly in the composition of their peripheral T cell compartment. To dissect the role of MHC and non-MHC genes in the development of peripheral T cell subsets in combination with susceptibility to CsA-AI the respective MHC congenic strains (LEW-1N and BN-1L) were examined for their T cell subsets and for their ability to develop CsA-AI. In this study we show that the Th1/Th2-like cell ratio as well as susceptibility to CsA-AI are under control of the non-MHC genes. This suggests that the Th1/Th2-like cell ratio is a critical determinant for development of CsA-AI. Alternatively, resistance can be attributed to lack of target organ susceptibility due to the absence of the target autoantigen in resistant rat strains. This interpretation is rejected, since both BN as well as BN-1L rats consistently develop the characteristic macroscopic and microscopic signs of CsA-AI upon adoptive transfer with autoreactive LEW-1N and LEW T cells, respectively. Therefore, it can be concluded that the non-MHC genes encode for immune deviation and thereby determine susceptibility or resistance to CsA-AI.

Fig. 1

Relative weight changes upon induction of CsA-induced autoimmunity (CsA-AI) in LEW rats (n = 10; •; (a)), BN rats (n = 10; ○; (a)), LEW-1N rats (n = 10; ▴; (b)), and BN-1L rats (n = 6; ▵; (b)). Results are presented as the mean (± s.d.) of the relative weights compared with the weight on the day of bone marrow transplantation. The weight loss on day 55 is significant (*P < 0.001; **P < 0.02; Mann–Whitney test) for both LEW and LEW-1N, respectively, compared with day 41, i.e. the day of disease onset.

Fig. 2

Development of clinical manifest CsA-induced autoimmunity (CsA-AI) in LEW rats (n = 10; •; (a)), BN rats (n = 10; ○; (a)), LEW-1N rats (n = 10; ▴; (b)), and BN-1L rats (n = 6; ▵; (b)). Clinical signs were scored on a scale from 0 to 3 depending on severity: 0, normal; 1, erythroderma; 2, dermatitis; 3, alopecia. Symbols represent single rats and bars represent the mean values.

Fig. 3

Production of cytokine mRNA in lymph node cells of LEW versus BN rats and the corresponding MHC congenic rat strains. The production of G3PDH, IL-2, IL-4, and IFN-γ mRNA was determined by reverse transcriptase-polymerase chain reaction (RT-PCR) upon stimulation of lymph node cells with phytohaemagglutinin for 18 h. Resultant PCR products were separated on an ethidium bromide-stained 2% agarose gel and visualized under UV light. The gels show the result of 25 and 30 PCR cycles in case of G3PDH, or 35 and 40 PCR cycles in case of IL-2, IL-4 and IFN-γ. The diagram is the result of a representative experiment out of a total of three experiments.