Complement receptors on normal human lymphocytes containing parallel tubular arrays.

Membrane complement receptors have been identified on a subpopulation of normal lymphocytes containing cytoplasmic inclusions called parallel tubular arrays (PTA) using two different rosetting techniques. The first technique utilizes as indicator cells erythrocytes that were coated with complement by the classic pathway of complement activation (EAC rosettes). The second technique utilizes as indicator cells Salmonella typhi, which were coated with complement by the alternate pathway of complement activation (FBC rosettes). In the latter technique, lipopolysaccharide material in the bacterial cell wall directly activates complement without the use of a sensitizing antibody. This eliminates binding of marker particles by lymphocytes having Fc receptors. The presence of PTA lymphocytes at the center of EAC rosettes and FBC rosettes was demonstrated by electron microscopy, indicating that the PTA lymphocyte has a complement receptor. Examination of FBC rosettes revealed that the adherent complement-coated bacteria were usually partially surrounded by pseudopodal extensions of the PTA lymphocyte. In addition, some PTA lymphocytes phagocytized the complement-coated bacteria but not the complement-inactivated bacteria. These phagocytic cells were placed in the lymphocytic series instead of the monocytic series by virtue of complete lack of endogenous peroxidase activity.