T cell-activating monokines in guinea pigs: comparison of high and low molecular weight factors

Guinea pig monokines produced by lipopolysaccharide-stimulated peritoneal macrophages were found in high (50,000-80,000) and low (10,000-30,000) molecular weight (m.w.) fractions by gel filtration. Both showed enhancing activity on the proliferative response of guinea pig and mouse thymocytes to PHA, but the high m.w. (65K) monokine was much more efficient than the low m.w. (15K) monokine in enhancing the response of lymph node T cells to PHA, suggesting its importance in the activation of peripheral T cells. The 65K monokine was coeluted with BSA present in the culture medium by DEAE-cellulose chromatography, but was clearly separated from it by hydroxylapatite chromatography. The immunoadsorption experiment with anti-BSA-coupled gel also indicated that 65K monokine is not a complex of low m.w. monokine with BSA. Our series of studies showed that most monokine activities were always found in the 65K fraction in guinea pigs. Thus, in guinea pigs, the 65K component appears to constitute a major class of T cell-activating monokines.