Action of Immune Serum on Meningeal H. Influenzae in vitro and in Experimental Infections

Freshly isolated meningeal strains of H. influenzae differ from most respiratory strains in their “smooth” colony forms and their virulence for rabbits and mice, and these closely correlated properties may be readily lost on subculture. † 1 , 2 In this instance virulence seems to be associated with ability of the organism to survive and multiply within the host's tissues, rather than with an “endotoxic” effect. In this laboratory filtrates and heat-killed cultures were found to be relatively innocuous to the test animals. Hence, there is little reason to look for “anti-endotoxic” properties in immune serums, and if such serums possess any protective or therapeutic value, this will probably be dependent on bactericidal action. There is reason to believe that a so-called “immune serum” may have little activity against a smooth virulent strain if the strain used for immunization is one which has become rough and avirulent. 1 , 2 , 3 In the course of my attempts to develop a product for the treatment of influenzal meningitis, tests were made of the bactericidal activity of various antibody preparations, and the results will be briefly presented.

Through the cooperation of Dr. L. T. Clarke of Parke, Davis and Company, several types of serum from immunized horses were prepared and used in these studies: (1) Felton antibody from a horse immunized against 2 meningeal strains of H. influenzae. One of these strains was “smooth” when first used in injecting the horses, but later became “rough”. The other was an old “rough” strain. (2) Serum from a horse immunized with a strain kept “smooth” by weekly intracisternal injections into rabbits. (3) Antibody from this serum concentrated according to the “Felton” method.