γδ T cell receptor repertoire in brain lesions of patients with multiple sclerosis

Abstract

The identification of activated T cells in the brains of patients with multiple sclerosis (MS) suggests that these cells are critical in the pathogenesis of this disease. Recently we have used the PCR method to analyse rearrangements of Vα and Vβ genes of the T cell receptor (TCR) in samples of MS and control brains. The results of these studies showed that TCR V gene usage in MS brains may be restricted and in particular that Vβ genes may be preferentially rearranged in certain HLA haplotypes associated with susceptibility to MS. In view of the recent evidence that T lymphocytes bearing the γδ chains may have autoreactive potential, we have assessed whether or not such TCR-bearing lymphocytes were also present in chronic MS lesions. TCR Vγ and Vδ were analysed by the PCR method using a panel of Vγ and Vδ primers paired with Cγ or Cδ primers in 12 MS brains, as well as in brain samples of ten normal post-mortem cases and three neurological controls. TCR VγCγ and VδCδ rearrangements were confirmed using Southern blotting and hybridisation of the PCR products with specific Cγ and Cδ probes. Only one to four rearranged TCR Vγ and Vδ transcripts were detected in each of the 23 brain samples obtained from 12 MS patients, with the majority of γδ T cells expressing the Vγ2 and Vδ2 chains. In marked contrast, Vγ and Vδ transcripts could only be found in one of the ten non-neurological control brains analysed. To assess the clonality of Vγ2 and Vδ2 T cell receptor chains in the brain samples of MS patients, we have sequenced the junctional regions of the TCR Vγ-N-Jγ-Cγ and Vδ-N-Dδ-N-Jδ-Cδ segments amplified from brain tissues, CSF and spleens of two MS patients and from the spleen of two control subjects. The sequence analysis obtained so far shows no compelling evidence of an MS specific expansion of one or more clones expressing particular types of γδ T cell receptors. In contrast, a clonal expansion of a different population of TCR γδ-bearing T cells was found in the spleen of both an MS patient and one of the control individuals. These results suggests that the γδ T cell response at the site ohronic lesions, involve a number of clones, possibly in response to several inflammatory antigenic stimuli. Whether or not γδ T cells are involved in the initiation of or in the chronicity of the disease remains to be elucidated.