Characterization of PPD-specific T-cell lines generated in type I (insulin-dependent) diabetic and healthy individuals.

The particular susceptibility to insulin-dependent diabetes mellitus (IDDM) conferred by HLA-DR3,4 heterozygosity has been suggested to be an effect of transcomplementation of HLA class II molecules. To test this hypothesis of special IDDM-specific hybrid determinants and to evaluate the T-cell repertoire towards a specific antigen in IDDM patients we generated a total of 352 PPD-specific T-cell lines by the soft-agar cloning technique and studied their restriction by HLA class II molecules. Of these lines, 227 were from nine IDDM patients, of whom six were DR3,4 heterozygotes, and 125 from 10 healthy controls. Forty-six T-cell lines elicited specific responses in at least two experiments and in addition to T-cell lines demonstrating class-II-restricted PPD specificity, lines with an alloreactivity occurred. HLA-DQ-restricted PPD-specific T-cell lines were not identified and a possible DP restriction (DPw2) was only observed with one line. These data indicate that PPD is preferentially presented to T cells in the context of HLA-DR/Dw. Presentation of PPD by hybrid molecules in IDDM patients or by IDDM-specific class II epitopes recognized by the T-cell lines was not demonstrated. By restriction fragment length polymorphism analysis using a probe for the joining region of the T-cell receptor gamma gene, T-cell lines generated by the soft-agar cloning technique were found to be oligoclonal. It is concluded that soft-agar cloning should be followed by subsequent limiting dilution in order to assure monoclonality. Different preparations of antigen-presenting cells (APC) were tested. In several cases the T-cell lines were not able to respond to PPD presented by Epstein-Barr-virus-transformed lymphoblastoid cell lines (LCL). It was demonstrated that lipopolysaccharides (LPS) of E. coli potently reduce the proliferative response of antigen-specific and alloreactive T cells when T-cell-depleted peripheral blood mononuclear cells (E- cells) were used as APC, whereas only limited inhibition was observed when LCL were used as APC in the presence of LPS. This effect of LPS is suggested to be mediated by increased prostaglandin secretion by monocytes among the E- cells since indomethacin abolished the effect of LPS. This observation may have implications for T-cell cloning procedures since we have found that most commercially available culture media are heavily contaminated with endotoxin.