BTLA and rheumatoid arthritis: These studies all suggest that the BTLA/HVEM/LIGHT co-signaling pathway is involved in the pathogenesis of RA, even though none of these studies measured the expression levels of BTLA, HVEM or LIGHT in T lymphocytes, which are all vital for the functional performance of the LIGHT/HVEM/BTLA co-signaling pathway [1, 21].