Functionally distinct high and low molecular weight species of channel catfish and mouse IL-1

Abstract

Culture supernatants from channel catfish monocytes exhibit IL-1-like activity for mouse and catfish T cells. Gel filtration analyses of these supernatants indicated that there were at least two forms of IL-1-like activity, i.e. a high molecular weight form (70 kD) active on channel catfish, but not mouse, T cells and a low molecular weight form (∼15 kD) with activity for mouse, but not catfish, T cells. Both sizes of catfish IL-1 exhibited α and β determinants as shown by Western blot analyses using antisera to human IL-1α and IL-1β. Further evidence for the IL-1 nature of these molecules was obtained by antibody inhibition assays wherein antisera to human IL-1α and IL-1β each neutralized ∼50% of the catfish activities, were additive to some extent, and could be reversed by the addition of the proper human recombinant protein. In culture supernatants of murine P388D 1 cells functional activities for catfish and mouse T cells were found only in high and low molecular weight fractions, respectively. Western blots with antiserum to mouse IL-1α revealed IL-1 determinants in both high and low molecular fractions of the mouse cell culture supernatants. These data suggest that catfish and mammalian IL-1 molecules may be quite similar with the caveat being that functional activity for catfish T cells requires a large protein, presented as an aggregate, a polymer, or simply a single chain 70 kD protein. However, only the low molecular weight forms (30 and 15 kD) are active on mouse T cells.