An assay for the detection of interferon dependent and interferon independent antibody activities

Systemic and ocular antibody responses to inactivated acute hemorrhagic conjunctivitis (AHC) virus; enterovirus 70 (EV70)

PURPOSE

Evaluate the immune response in rabbits injected with EV70, the agent of acute hemorrhagic conjunctivitis (AHC) and AHC associated neuropathy.

METHODS

Rabbits were injected intramuscularly with uv-light inactivated EV70 isolate J670/71. Neutralizing activity against EV70 was quantified in serum and tear samples and the immunoglobulin (Ig) classes of the neutralizing activity in serum identified by sucrose gradient ultra-centrifugation. Adjuvant muramyl dipeptide (MDP) was applied topically to assess the role of ocular inflammation on levels of neutralizing antibody, proteins and Ig in tears. The protective effects of human and rabbit sera and interferon-alpha (IFN-alpha) against EV70 were compared in human conjunctival and lens cells.

RESULTS

Sera collected at 6 and 13 d contained 19S IgM anti-EV70 neutralizing antibody, while serum collected 21 d post injection contained 19S IgM and 7S IgG anti-EV70 neutralizing antibody. Low titers of anti-EV70 activity (< or =30 U/ml) were detected in tears of seropositive rabbits. MDP induction of conjunctivitis in seropositive rabbits increased tear IgG concentration (3-fold) and anti-EV70 neutralizing antibody titers (> or =10-fold). The protective effect of the rabbit and human sera against EV70 infection in conjunctival, but not lens epithelial cells, was enhanced by the addition of IFN-alpha.

CONCLUSIONS

Immunization with uv-light inactivated EV70 elicits a classical humoral immune response in rabbits. The protective activity of serum in EV70-infected human conjunctival cells, but not lens cells, was increased by IFN-alpha. Adjuvant MDP-induced conjunctivitis, increased blood-conjunctival barrier (BCB) permeability and anti-EV70 neutralizing activity in tear of seropositive rabbits. The results suggest immunization with inactivated EV70 could provide systemic as well as ocular protection during natural EV70 infection.

Stereo-isomer specific induction of renal cell apoptosis by synthetic muramyl dipeptide (N-acetylmuramyl-L-alanyl-D-isoglutamine)

The cytotoxicity of bacterial cell wall components, muramyl dipeptide (synthetic N-acetylmuramyl-L-alanyl-D-isoglutamine; L,D-MDP) and lipopolysaccharide (LPS), was investigated in several kidney cell lines. MDP and LPS were toxic to rabbit and monkey kidney cells, MDP was toxic to canine kidney cells, but not to human or porcine kidney cells. Notably, L,D-MDP was >100-fold more cytotoxic/microg than the D,D-MDP and L,L-MDP, as well as LPS. L,D-MDP and analogs containing L,D-MDP were the most widely cytotoxic of the MDP tested. The MDP-induced cytotoxicity was characterized as apoptosis by DAPI staining and DNA laddering. The acute rabbit kidney (RK13) cell apoptosis (cell death in < 5 h) induced by apical or basal application of MDP was associated with glutamate (Glu) release, decreased gamma-glutamyltranspeptidase (GGT) and acidosis and was suppressed by Indomethacin, Naproxen and Curcumin. The cytotoxic activity of L,D-MDP was decreased significantly by 24 h incubation in human sera. Aged (> 2 year-old) rabbits that apparently failed to quickly clear and excrete a uveitogenic dose of MDP within 24 h died in I week. The results indicate that minute amounts (5 ng/ml) of MDP containing L-alanyl-D-isoglutamine can induce renal cell apoptosis in vitro and support MDP-induced kidney cytotoxicity in rabbits. Also, the results indicate that MDP in sera can be detected utilizing the RK13 cell bioassay and that failure to rapidly clear and excrete L,D-MDP is associated with uveitis and death in aged rabbits.

Antibodies may act synergistically or additively with interferon to inhibit poliovirus

We investigated the protective effects of combinations of interferon-alpha (IFN-alpha) and neutralizing monoclonal antibodies (mAbs) and serum antibodies against poliovirus type 1 (PV-1) in vitro. Our results indicate that the antiviral effects of IFN-alpha and most neutralizing mAbs to PV-1 act synergistically to inhibit PV-1. However, the antiviral effects of IFN-alpha and one type specific mAb to PV-1 were additive. Further, the protective effects observed with combinations of IFN-alpha and rabbit, monkey or human serum containing effects observed with combinations strains Mahoney (Mah) and Sabin (Sab) were similar to those observed with combinations of IFN-alpha and mixtures of mAbs with synergistic and additive activities. Our studies suggest that the antiviral activity of neutralizing antibody acts with the antiviral activity of IFN to inhibit virus infection synergistically or additively and that the different antibody activities are associated with the mechanism of neutralization.