INTENDED USE

This Human IFN-γ ELISA kit is to be used for the in vitro quantitative determination of concentrations in serum, plasma, cell culture supernatant, and other biological fluids. This kit is intended FOR LABORATORY RESEARCH USE ONLY and is not for use in diagnostic or therapeutic procedures.

INTRODUCTION

Interferon gamma (IFN-γ) is a multifunctional protein first observed to have antiviral activity in cultures of Sindbis virus-infected human leukocytes stimulated by PHA. ⁽¹⁾⁾ The biochemistry and biological activities of the interferons have been extensively reviewed.Produced by both CD4⁺ and CD8⁺ T lymphocytes and natural killer (NK) cells, INF-g is now known to be both an inhibitor of viral replication and a regulator of numerous immunological functions. IFN-g influences the class of antibody produced by B cells up-regulates classes I and II MHC complex antigens and increases the efficiency of macrophage-mediated killing of intracellular parasites. ^{(2, 3)} Most of the activities attributed to IFN-γ are believed to be mediated by IFN-γ-induced proteins. The appearance of such proteins is a consequence of IFN-γ binding to a specific receptor that is distinct from the receptor for IFN-a and b. ⁽⁴⁾ Human IFN-g is reported to be active only on human and non-human primate cells. ⁽⁵⁾ The biochemistry and biological activities of the interferons have been extensively reviewed. ^(2-9)

Human IFN-γ is a 143 amino acid residue glycoprotein with MW of 20 or 25 kDa that demonstrates little sequence homology to IFN-αand β. ^(10-13) Naturally occurring IFN-γis found as either of two molecular-weight-species, differing in degree of glycosylation. The 25 kDa species is glycosylated at both potential N-linked glycosylation sites on the molecule (Asn 25 and 97), while the 20 kDa species is glycosylated only at Asn97. ^{(17, 18)} In neither case glycosylation is required for biological activity. ^{(13, 16)} Two allelic variants of IFN-γ have been described differing by the presence of an Arg or Gln at position 137. ^{(10, 16)}

Although the cDNA encoding for IFN-γ predicts a protein of 146 amino acid residues, the form secreted by mammalian cells shows a truncation of three amino acid residues from the N-terminus and the conversion of the fourth residue from glutamic acid to pyroglutamate. ⁽¹¹⁾ The secreted form of IFN-γ has no potential for the formation of disulfide bonds. ⁽¹³⁾ Human IFN-γapparently exists as a head-to-tail dimmer in solution with the C-terminus of one monomer aligned with the N-terminus of the other monomer. ^{(18, 19)}

IFN-γ possesses a variety of functions. Produced by CD8+, NK and TH2 T helper cells, IFN-γ has documented antiviral, antiprotozoal and immunomodulatory activities, ^(20-24) although IFN-α and IFN-β seem to have more potential antiviral activities than IFN-g. ⁽²⁴⁾ The antiprotozoal activity of IFN-g against Toxoplasma and Chlamydia is believed to result from indoleamine 2, 3-dioxygenase activity, an enzyme induced by IFN-g. ⁽²⁵⁾ The immunomodulatory effects of IFN-g are extensive and diverse. In monocyte/ macrophages, IFN-γ increases expression of class 1 MHC antigens; increases the production of IL-1, platelet-activating factor, H₂O₂, and pterin; protects monocytes against LAK cell-mediated lysis; down-regulates IL-8 mRNA expression that is up-regulating TGF-b receptor expression and up-regulating expression of the IL-2Rg subunit. ^{(23, 25, 26-29)} It has also been demonstrated to be chemotactic for monocytes but not neutrophils. ⁽³⁰⁾ IFN-γ selectively enhances both Ig G_2a secretion by LPS-stimulated B cell activation. ^{(31, 32)} IFN-γ has also been reported to induce its own expression. IFN-γ production accompanying local inflammation results in the induction of IFN-γ mRNA synthesis at distant sites. This effect could be due to circulating IFN-γ or the production of IFN-γ by migrating cells ⁽³³⁾. IFN-γhas also been shown to up-regulate ICAM-1 but not E-selectin or VCAM-1 expression on endothelial cells ⁽³⁴⁾. Finally, IFN-γ has recently been implicated in the development of a cholinergic phenotype in embryonic septal neurons. In cultures of rat septal nuclei, IFN-γ induced the development of cholinergic neurons.

This IFN-γ ELISA is a 2.5 hour solid phase immunoassay readily applicable to measureIFN-γ levels in serum, plasma, cell culture supernatant, and other biological fluids in the range of 0 to 1600 pg/mL. This IFN-g ELISA recognizes both natural and recombinant human IFN-γ and exhibits no detectable cross-reactivity with human; SAA, EGF, IL-6, IL-8, IL-16, M-CSF, GM-CSF, TGF-β₁, RANTES, FGF, MIP-1α, CRP, EPO. It is expected to be effectively used for further investigations into the relationship between IFN-γ and various diseases.