Arthritis Susceptibility and Tolerance in Collagen Transgenic Mice

This thesis is based on work trying to understand the normal and pathological interactions taking place between the immune system and cartilage, specifically involving the cartilage-specific protein typ II collagen (CII). The work has been carried out in an experimental model of rheumatoid arthritis namely collagen type II induced arthritis (CIA) in mice. CIA can be triggered in mice of certain MHC class II haplotypes, H-2q and H-2r, and is T-cell dependent. The mice are typically immunized with foreign CII, such as rat CII, to trigger disease. After sequencing rat CII, 12 out of 1015 amino acids differed compared to mouse CII. One of the differences is located at position 266, which is within the crucial T-cell epitope CII 256-270. Interestingly, this T-cell epitope contains post-translational modifications which include hydroxylation of prolines and lysines as well as glycosylations of the hydroxylysines. Glycosylated rat CII is more arthritogenic than deglycosylated. To study T-cell regulation of a known H-2q binding peptide involved in disease, transgenic mice that expressed the rat version of the T-cell epitope was produced. Three transgenic systems have been used. 1) Mice expressing the rat epitope in type I collagen, i.e. in skin and bone. This systemic expression led to an increased accessability of transgenic collagen to the immune system. The transgenic mice were tolerant to CIA, and did not develop detectable immune responses to rat CII. Thus, the CII 256-270 epitope is clearly immunodominant. 2-3) The rat epitope was also transgenically expressed in a cartilage specific manner, leading to restricted interactions between the immune system and transgenic collagen. The transgenic mice showed an incomplete tolerance to CIA, and developed measurable immune responses to rat CII, although the T-cells proliferated poorly. Development of CIA was not dependent on recently exported T-cells from the thymus. Human CII contain the same CII 256-270 epitope as rat CII. Transgenic mice expressing human CII in cartilage was also investigated, the mice could mount immune responses to CII and some of them also developed arthritis. These three systems have been used to study tolerance, breakage of tolerance and disease development. Lastly, the issue of tissue quality has also been addressed by the use of a transgenic mouse with a deleted form of CII, which developed chronic arthritis after CII immunization. My work demonstrate that the immune system normally develop tolerance to our own cartilage antigens, but that tolerance can be broken and arthritis develops. Further studies on different ways of breaking tolerance will be beneficial in understanding the pathogenesis of diseases such as rheumatoid arthritis