Identification and purification of a receptor on macrophages for the dengue virus‐induced suppressor cytokine

SUMMARY Dengue type 2 virus (DV)‐induced suppressor cylokine (SF) binds to macrophages to transmit the suppressor signal to recruit the second subpopulation of suppressor T cells. The present study was undertaken to identify and purify the receptor for SF(SF‐R) on macrophages. The binding of 125 1‐SF to macrophages was saturable and reversible. Scatchard analysis showed the presence of both high (54 000/cell) and low (178 × 10 6 /cell) affinity receptor sites. The binding of 125 I‐SF to macrophages was inhibited by pretreatment of macrophages with anti‐SF antiseruin but not by a heterologous antiserum. Normal mouse peritoneal macrophage membrane was solubilized withTriton‐X‐100 and the components separated by low pressure liquid chromatography (LPLC) to purify SF‐R. The presence of SF binding moiety (SF‐R) was screened at each step of purification. The purified SF‐R resolved into two bands of 45–50 kD mol. wt on SDS‐PAGE. 125 I‐SF + SF‐R complex run on SDS‐PAGE showed a single band at about 55–60 kD mol. wt by autoradiography. Anti‐SF‐R anti serum reacted with SF‐R in a Western blot test; the reaction was abolished by pretreatment of the blots with proteinase K, but not by pretreatment with periodic acid. SF‐R was composed of two polypeptide chains (α and β) which were obtained in pure form by high performance liquid chromatography (HPLC) of dithiothreitol‐ and iodoacetamide‐treated SF‐R. Only the β chain bound SK.