Mice previously infected with an aerosol of A/Rec 31 influenza virus were strongly protected against an aerosol challenge with A/Vic influenza as judged by lung virus titers recovered 2 days after the challenge infection. Such complete homotypic immunity was not achieved by priming with live Rec 31 virus injected i.v. or UV-inactivated Rec 31 virus administered s.c. together with Al(OH)3 and saponin. The reason for the superior protective effect of the natural infection was investigated. The protection induced by respiratory infection with Rec 31 virus was specific for influenza A viruses. It was not correlated with specific serum hemagglutination inhibition antibody titer or cross-reactive cytotoxic T (Tc) cell reactivity. Moreover, the transfer of splenic and lymphoid T cell populations with strong secondary Tc activity did not significantly reduce lung virus titers in recipient mice 3 days after infection. The protection however occurred in parallel with the presence of cross-reactive IgA antibody in the lung washings. It thus appears that local secretory IgA plays a causal role in the prevention of cross-infection by influenza A virus. Serum antibody and Tc cells, on the other hand, may be crucial for recovery from such infection. All mice primed with live Rec 31 virus, administered i.v. or by aerosol and expressing equally high levels of Tc reactivity, survived a lethal challenge with A/PR8 virus. The same challenge, however, killed half of the mice immunized s.c. with inactivated Rec 31 virus which induced only a low level of Tc reactivity.

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SUMMARYA single radial haemolysis in gel technique has been developed for the detection and measurement of antibody to influenza haemagglutinin. The method combines the sensitivity of haemagg]utination-inhibition with the accuracy of single radial diffusion. It is simple, quick, reproducible, does not require purified or concentrated virus, and is unaffected by non-specific inhibitors. The method is particularly suitable for the routine screening of large numbers of serum samples, and may have application also to viruses other than the influenza group.

Fourteen neutralizing monoclonal antibodies recognizing human rhinovirus (HRV) type 2 have been used to select a total of 51 virus escape mutants. Crossresistance analysis of the mutants, together with RNA sequencing and identification of amino acid substitutions, have revealed three neutralization sites on the virus surface. Two of these appear to correspond to the NIm-IA and NIm-II sites described for HRV-type 14, although there are also substantial differences. The third site has not been described previously.

Heart-reactive antibody is known to be produced in animals immunized with group A streptococci. However, the detection and quantitation of these antibodies and their respective antigens have been limited to immunofluorescence or immunoprecipitation tests. In this study a more sensitive technique was used to detect heart-reactive antibody, i.e., the enzyme-linked immunosorbent assay (ELISA). Countercurrent immunoelectrophoresis and agar gel immunodiffusion were also used to confirm the reactivity of rabbit antisera to group A streptococci and human heart tissue. Human heart tissue antigen was prepared by Triton X-100 extraction, and checkerboard titrations of heart tissue antigen versus streptococcal antisera revealed optimal concentrations of each for the ELISA. When immune rabbit serum was reacted with heart tissue antigen, a 5to 10-fold increase was observed over the reactions of preimmune sera controls. Streptococcal antiserum was found to have a sixto eightfold greater reactivity with heart tissue antigen than with similar concentrations of kidney and skeletal muscle antigens. Heart tissue antigen was partially purified by DEAE-cellulose chromatography, and quantities of >10 to 100 ng (dry weight) were shown to react with streptococcal antisera in the ELISA. Heart, kidney, and skeletal muscle antigens were subjected to electrophoresis in polyacrylamide gel slabs and blotted onto a nitrocellulose filter. These filter blots reacted with streptococcal antisera and confirmed the tissue antigen specificity observed with the ELISA. In addition, the ELISA was found to be an effective method for the detection of heart-reactive antibodies produced by murine hybridomas that were producing antibody to group A streptococci.