Myelin basic protein (MBP) is a well-characterized autoantigen potentially involved in the pathogenesis of the most common human demyelinating disease of the central nervous system (CNS), multiple sclerosis (MS). It is known that MBP-specific T-cell responses differ widely among different individuals and also within a single donor in terms of fine specificity and functional characteristics including the avidity in antigen recognition. In this report, we demonstrate that the in vitro selection of MBPreactive T-cell repertoire is strictly dependent upon the antigen dose used in the primary cultures. MBP-specific T-cell lines (TCLs) were generated from MS patients and healthy donors using different antigen concentration in cultures (0.1 to 50 g/ml). In both MS patients and controls, the number of obtained T-cell lines was affected by the antigen concentration. In addition, low and high antigen concentrations selected in vitro different T-cell populations in terms of peptide specificity patterns and different functional avidities in antigen recognition. Low concentrations of MBP in the primary cultures yielded a small number of TCLs recognizing the specific antigen with higher avidity whereas high antigen concentrations allowed the in vitro expansion of a higher numbers of T-cells recognizing MBP with lower avidity. The use of different antigen concentrations in the primary cultures can be applied as a simple experimental system to investigate the overall avidity repertoire of antigenspecific T-cell response in humans.