- The 16/6 anti-DNA idiotype (id) is a pathogenic idiotype first identified on a human hybridoma antibody derived from a patient with systemic lupus erythematosus (SLE). The SA-1 anti-DNA, which antibody was established in a similar fashion from a patient with polymyositis, also carries the 16/6 id, although it has a greater reactivity with dsDNA. The presence of the 16/6 id as defined by anti-16/6 and anti-SA-1 was determined in 3 distinct populations of patients with SLE: 502 Mexicans, 98 English (including Caucasians, West Indians, Chinese, Asians) and 93 Israelis. A similar prevalence (around 20%) of the 2 idiotypes was found, with a significant overlap. The latter finding was supported by a significant correlation noted between the prevalence of the 2 idiotypes (r = 0.58 p less than 0.001). Despite the fact that 16/6 antibody is most probably encoded by a germline gene, thus being genetically determined, no distinction in the prevalence of the ids could be detected between completely different populations of patients with SLE. This finding may support the independent pathogenic role ascribed to the 16/6 id.