Expression of GPI-Anchored Complement Regulatory Proteins CD55 and CD59 Differentiates Two Subpopulations of Human CD56+CD3- Lymphocytes (NK Cells)

CD55 and CD59 are both glycosylphosphatidylinositol (GPI)-anchored complement regulatory proteins found on the surface of most hemopoietic cells. Using three-color cytofluorographic analysis with antibodies recognizing CD56, CD3, and CD59 or CD55 we determined that CD56+CD3- lymphocytes (NK cells) expressed both CD55 and CD59 but at lower levels than CD3+ lymphocytes. Since the CD56+CD3- lymphocyte population is heterogeneous, we examined expression of CD55 and CD59 on selected CD56+CD3- iymphocyte populations by depleting peripheral blood leukocytes of T cells, B cells, and monocytes. Dual staining of the selected CD56+CD3- cells, which were >95% CD56+, permitted the distinction of two subpopulations: a major CD16brightCD56dimCD55dimCD59dim subpopulation and a minor CD16dim/negCD56brightCD55brightCD59bright subpopulatlon. Treatment with phosphatidylinositol-specific phospholipase C released both the CD55 and CD59 antigens from the surface of CD56+CD3- cells, indicating that both are GPI-anchored, as they are on other lymphocytes. CD56+CD3- cell subpopulations were individually isolated by anti-CD55 or anti-CD16 negative selection and were functionally compared to the parent CD56+CD3- cell population. The CD16brightC-D56dimCD55dimCD59dim cells killed NK targets well but did not proliferate well in response to rIL-2, whereas CD16dim/negCD56brightCD55brightCD59bright cells proliferated well in response to rIL-2 but did not kill NK targets efficiently. We conclude that all CD56+CD3- cells express some levels of the GPI-anchored proteins, CD55 and CD59, and that two CD56+CD3- subpopulations with different functional characteristics can be distinguished by the level of expression of these two antigens.