Anti-Thy-1 plus complement-treated, cultured bone marrow cells resemble fetal thymocytes in killer cell function and marker expression.

Anti-Thy-1.2 plus complement treated bone marrow cells were tested after short-term culture for their ability to lyse allogeneic target cells. Significant lytic activity was generated after 9 days, and required both CAS and splenic or PEC feeders as culture supplements. Allogeneic as well as syngeneic-specific cytotoxic cells were generated polyclonally under such conditions, and could be separated by using limiting dilution protocols. When 65 clones were tested for lytic activity toward three targets bearing H-2k, H-2d, and H-2b haplotypes, respectively, only two clones lysed all three targets; 53 clones showed specificity toward one target only. Targets low in class I H-2 expression were lysed only minimally compared with high H-2 expressors. Allogeneic-kill by C57BL/6 bone marrow cells grown on AKR feeder cells was destroyed by treating effectors with anti-Thy-1.2, but not anti-Thy-1.1, antibody plus complement, suggesting 1) a de novo generation of surface Thy-1 during culture and 2) that effectors were derived from bone marrow, but not feeder, populations. Partial inhibition of kill occurred by treatment of effectors with anti-asialo-GM1 (approximately 80%), anti-Lyt-2 (approximately 60%), or anti-Ly-5.1 (approximately 30%) antibodies plus complement; treatment of effectors with anti-L3T4 or anti-NK-1.1 antibodies plus complement had no effect. When precursor populations were treated with either anti-Thy-1.2 alone or a combination of anti-Thy-1.2 and anti-Lyt-2 antibodies plus complement, killers were easily demonstrated. However, the addition of an anti-asialo-GM1 antibody plus complement treatment before culture abolished function. The characteristics of these effectors showed a resemblance to those described previously for day 14 to 17 fetal thymocytes, designated pCTL.