Ribosomal protein L7 included in tuberculin purified protein derivative (PPD) is a major heat-resistant protein inducing strong delayed-type hypersensitivity

The tuberculin purified protein derivative (PPD) is a widely used diagnosti c antigen for tuberculosis. It consists of more than 100 denatured proteins in a culture filtrate of a heated culture of Mycobacterium tuberculosis. I n two-dimensional electrophoretic analysis of PPDs from M. tuberculosis and M. bovis BCG, most proteins were diffusely separated and could not be seen as spots because of denaturation, whereas a few proteins showed relatively clear spots, indicating heat resistance. Two such proteins corresponded to ribosomal proteins L7 and L12. The mixture of these proteins L7/L2 induced a strong delayed-type hypersensitivity reaction. Another protein showing a clear spot was a GroES analogue, but this did not induce delayed-type hype rsensitivity. There were a few other unidentified proteins. It is well know n that L7 and L12 are encoded by the same gene and that they differ from ea ch other only by an acetylic post-translational modification that occurs at the N-terminus of L12 converting it to L7 in Escherichia coli. L12, but no t L7, was found in two-dimensional electrophoresis of BCG ribosomes, althou gh we found two proteins corresponding to L7 and L12 in PPDs and a native c ulture filtrate of BCG. We compared the delayed-type hypersensitivity react ion elicited by L7/L12 derived from a culture filtrate of BCG and L12 deriv ed from BCG ribosomes. L7/L12 from the culture filtrate could induce delaye d-type hypersensitivity, but L12 from ribosomes could not, indicating that L7 was attributable to the induction of delayed-type hypersensitivity. The activity of L7/L12 was heat resistant. Neither glycosylation nor phosphoryl ation of L7/L12 from a culture filtrate could be detected. The acetylation at N-terminal of L12 was essential for the delayed-type hypersensitivity ac tivity.