Mycobacteria are known to induce autoimmune response in the host. Anti-host keratrin
antibodies (AkAbs) might be responsible for the autoimmune phenomena in
leprosy patients as majority of
leprosy lesions are manifested in the skin and occurrence of
keratosis is not an uncommon feature. The aim of this study was to find out the level of AkAbs in
leprosy patients across the spectrum and to explore its correlation with the clinical manifestation of the disease. Further, mimicking
epitopes of
keratin and Mycobacterium leprae components were characterized. We screened 140
leprosy patients (27 BT, 28 BL, 41 LL, 25 T1R, 19 ENL), 74 healthy controls (HC) and 3
psoriasis patients as positive control. Highest AkAbs level was observed in the
psoriasis patients followed by T1R, LL, BL, ENL, TT/BT. AkAbs level was significantly (p<0.05) higher in all the groups of
leprosy patients except TT/BT in comparison to HC. Significant positive correlation was found between number of lesions and level of AkAbs in
leprosy patients. Highest lympho-proliferation for
keratin protein was observed in T1R, followed by BL/LL, TT/BT, ENL. Lympho-proliferation was significantly (p<0.05) higher in all groups of
leprosy patients except ENL in comparison to HC. Interestingly, it was noted that hyperimmunization of inbred strains of female BALB/c mice and rabbit with M. leprae soluble
antigen (MLSA) induce higher level of AkAbs. The percentage of FoxP3(+) expressing Treg cells (total CD4(+)CD25(+)FoxP3(+) andCD4(+)CD25(+hi)FoxP3(+)) in splenocytes and lymph nodes of hyperimmunized mice were declined in comparison to control mice. Further, it was found that this autoimmune response can be adoptively transferred in naïve mice by splenocytes and lymph node cells as well as T cells. Comparative molecular characterization between
keratin and MLSA noted a cross-reactivity/similarity between these two
antigens. The cross-reactive
protein of
keratin was found to be in molecular weight range ≈74-51kDa and at pI 4.5 while the cross-reactive
protein of MLSA was found to be in molecular weight ≈65kDa and at pI 4-4.5. Cross-reactive
protein of
keratin and MLSA was identified and characterized by MALDI-TOF/TOF analysis and Mascot software. It was found that the
keratin (host
protein) which reacted with anti-M. leprae sera is cytokeratin-10 and MLSA which reacted with anti-
keratin sera is
heat shock protein 65 (HSP 65). Seven
B-cell epitopes of cytokeratin-10 and HSP 65 was found to be similar by multiple sequence alignment using ClustalW server and out of which 6
B-cell epitopes were found to be on the surface of HSP 65. In conclusion, our study provides evidence for the existence of molecular mimicry between cytokeratin-10 of
keratin (host
protein) and 65kDa HSP (groEL2) of M. leprae. Presence of heightened CMI response of
leprosy patients to
keratin and positive correlation of AkAbs level with number of lesions of
leprosy patients showed the clinical evidence for its role in the pathogenesis in
leprosy.