Soluble Factors Containing Thy-1 Antigen Shed from Lymphoblastoid Cells Modulate in vitro Plaque-Forming Cell Response

Abstract

Culture media from two lymphoblastoid cell lines, BW 5147 (Thy-1.1, H-2^k) and S.49.1 (Thy-1.2, H-2^d), were capable of suppressing approximately 50% of the primary in vitro anti-SRBC hemolytic plaque response of BALB/c (Thy-1.2, H-2^d) and AKR (Thy-1.1, H-2^k) spleen cell cultures. The association of the Thy-1 molecule with the suppressor factor was suggested when pretreatment of both of these conditioned media with either anti-Thy-1.1 or anti-Thy-1.2 alloantisera abrogated the modulatory activity. Simultaneous measurement of primary anti-Thy-1.1 PFC responses by the same BALB/c (Thy-1.2, H-2^d) spleen cell cultures indicated that only BW 5147 culture medium could induce a significant anti-Thy-1.1 antibody response. In contrast to neutralization of suppressor activity by both anti-Thy-1 alloantisera, only anti-Thy-1.1 sera adsorption of BW 5147 culture medium abrogated the anti-Thy-1.1 PFC response; anti-Thy-1.2 sera either had no effect or enhanced it.

The molecular properties of the suppressor factor and shed Thy-1 were analyzed by column chromatography of culture medium from [³H]glucosamine-labeled S.49.1 and BW 5147 cells. The suppressive activity in culture medium from both tumor cells was found in fractions of high m.w. (>2 × 10⁶ daltons). Immunoprecipitation techniques and the anti-Thy-1 PFC assay were utilized to demonstrate that in both neoplastic cell lines the Thy-1 antigenicity also resided primarily in large m.w. complexes of >2 × 10⁶ daltons. Column fractions containing high m.w. substances from BW 5147 or S.49.1 culture medium, either by themselves or pretreated with anti-Thy-1.1 or anti-Thy-1.2 sera, were cultivated with BALB/c spleen cell cultures and gave results similar to those observed with unfractionated culture medium. These experiments indicate that the suppressor activity found in the conditioned medium of these two lymphoblastoid cells is contained in a high m.w. complex associated with the Thy-1 antigen.