Objectives To study the Lymphocytotoxic antibodies (LCA) in SLE patients and their first degree relatives compared to matching controls.

Methods Complement dependent microcytotoxicity test was used to assess the presence of LCA, their temperature dependence in addition to HLA specificity among 40 SLE patients, 184 of their first degree relatives in comparison to 100 subjects of a blood bank donor as a healthy control.

Results Lyphocytotoxic activity was manifested in 70% of patients, 33.36% of relatives compared to 80% of control group. While cold dependent antibodies were higher among patients group (92.8%) compared to 35% of their relatives. The presence of these antibodies in a control group was less temperature dependent, since 62.5% of them reacted both at 22C° and 15C° and only 12.5% of them exhibited a sole reactivity of 15C°.

No association between LCA and and of HLA antigen of both classes was detected, however, patients had a tendency to react with a large number of lymphocyte samples than did positive sera from other group. Generally, females had a higher percentage of LCA (42.15%). Yet, the highest percentage was reported among sisters, followed by mothers, while brothers exhibited the least frequency (15.15%). In contrast to females, male subjects reported the highest frequency of these antibodies among age group of > 50 years.

Conclusion Patients expressed a high positivity rate of cold LCA. Moreover, female first degree relatives showed higher positivity rates than male relatives or controls.