Allelic Class II Determinants Defined by PLT Typing
The HLA-D/DR region in man is complex, containing several closely linked genes which control a number of different cell surface antigens. Among these, some determinants can be detected by primed lymphocyte typing (PLT). In the present study, 50 PLTs were generated between pairs of healthy individuals sharing the same DR allele and, in 2 cases, a blank allele at the DR locus. The PLTs were obtained using classic techniques  and were tested against a panel of 81 normal individuals typed for HLA-DR (DRl-w10) and, in some cases, also for DP. Comparisons were also made with DNA restriction fragments using a ß DQ probe. The PLT activity was extremely reliable, using 25 × l03 PLT cells against 1 × 105 restimulating cells. The level of MLC reactivity (10,000–25,000 cpm) appeared to be predictive of the PLTs obtained: reliable results were observed only in the case of reactive reagents giving ≥ 10,000 cpm. The nine PLT reagents (single or clusters), selected because they demonstrated a pattern of reactivity, recognized five allelic determinants (no triplets) and were correlated (P < 10−8) with splits of DR specificities: short DR3 (PLTs 24, 40, 41), short DR5 (PLTs 26, 22, 42); and with two different parts of DRw6 (PLT 9 and PLT 10). (The patterns against 50 cells are shown in Fig. 1.) The determinant recognized by PLT 9 is correlated (P = 0.003) with a split of DQwl determined by ß DQ restriction fragments. No correlation with the pattern given using specific PLTs developed against DPwl - 5.