The antichlamydial, antiviral, and antiproliferative activities of human gamma interferon are dependent on the integrity of the C terminus of the interferon molecule

Abstract

The effects of recombinant human gamma interferon (rHuIFN-γ; two identical monomers of 140 residues in length) and of two re-engineered C-terminal variants, rHuIFN-γ Tetra-Ser (residues 129 to 132 replaced by serine) and rHuIFN-γ 125 (two identical monomers of 125 residues each with the last 14 residues plus an additional alanine from the C terminus deleted), were compared in terms of several in vitro biological activities. By using three different human cell lines (HeLa 229, HEp-2, and A549), the interferons were tested for their ability to inhibit: (i) growth of Chlamydia trachomatis; (ii) replication of encephalomyocarditis virus; and (iii) cell growth. rHuIFN-γ restricted the growth of chlamydiae to 50% of the non-IFN-treated control at concentrations ranging from 0.01 to 0.05 ng/ml, depending on the cell type assayed. One of the modified proteins, rHuIFN-γ Tetra-Ser, also decreased the growth of chlamydiae, but it required a concentration of approximately 0.5 ng/ml to produce 50% inhibition. rHuIFN-γ 125 had the lowest antichlamydial activity of the three IFN-γ variants tested; concentrations of 1 to 20 ng/ml were needed to reduce the growth of C. trachomatis to 50% of that of the control. The relative antiviral and antiproliferative activities of the three IFN-γ preparations paralleled their antichlamydial activities in these three cell lines. The antiencephalomyocarditis virus activities o rHuIFN-γ Tetra-Ser and rHuIFN-γ 125 were reduced by approximately 10-fold and 102- to 103-fold, respectively, compared with the antiviral activity of rHuIFN-γ. Proliferation of the three cell lines was restricted to approximately 50% of the control with 0.5 to 10 ng of rHuIFN-γ per ml. Inhibition of cell growth by rHuIFN-γ Tetra-Ser was significant only at concentrations equal to or greater than 30 ng/ml, and the rHuIFN-γ 125 variant did not significantly decrease the growth of any of the three cell lines at the concentrations tested. These results suggest that the C-terminal portion of rHuIFN-γ is critical for maintaining the conformation necessary for inducing the antichlamydial, antiviral, and antiproliferative activities of the molecule.