SOLUBLE CYTOKINE RECEPTORS IN HUMAN COLOSTRUM AND MILK. ▴ 1816

Abstract

We examined random and longitudinally collected specimens of human colostrum & milk for interleukin-1 receptor antagonist (IL-1RA), soluble interleukin-6 receptor (sIL-6R), and soluble forms of TNFα receptors I and II (TNF RI and TNF RII) using ELISA and EASIA (Enzyme Amplified Sensitivity Immunoassay) methods. By ELISA, random samples of both colostrum& milk contained IL-1RA [672 ± 202 pg/ml ([horizontal bar over]x ± SE), n = 20, and 717 ± 248 pg/ml, n = 15, respectively], sIL-6R [12761 ± 982 pg/ml, n = 22, and 2436± 580 pg/ml, n = 15], sTNF RI [> 3703 ± 305 pg/ml, n = 24, and 1732 ± 208 pg/ml, n = 18], and sTNF RII [> 4507 ± 770 pg/ml, n = 25, and 931 ± 104 pg/ml, n = 18). Both colostrum & milk sTNF RI levels were higher than plasma levels (824± 82 pg/ml, n = 18, p < 0.05 vs colostrum or milk), while only colostrum levels of TNF RII were higher than plasma (1518 ± 90 pg/ml, n= 19, p < 0.05 vs. colostrum). Longitudinal samples from 7 women (up to 200 days of lactation) showed similar results, with sTNF RI levels maintained throughout. ELISA measured “free” TNFα in longitudinal specimens was low (3 ± 1 pg/ml, n = 79), while EASIA-based measurements of “total” TNFα in the same specimens were 30-fold higher(99 ± 20 pg/ml, n = 87). Column chromatography showed that colostrum and milk sTNF RI and RII were larger (30-55 kDa) than expected, suggesting association with other components. The data show colostrum & milk are rich in soluble forms of TNFα receptors and suggest that TNFα in colostrum and milk may be soluble receptor-bound.