The properties and chemical nature of the psittacosis virus hemagglutinin

Abstract

1. 1. The 6BC strain of psittacosis virus produced a murine erythrocyte hemagglutinin which closely resembles the hemagglutinins of meningo, feline, and murine pneumonitis viruses. 2. 2. Adsorption of the psittacosis virus hemagglutinin to murine erythrocytes was compared to the nonspecific adsorption of this substance on inorganic adsorbents. The adsorption of the hemagglutinin on the inorganic materials was instantaneous and occurred equally well in the presence or absence of the calcium ion. Specific adsorption of the hemagglutinin on the murine erythrocyte was found to be a progressive process requiring 25 minutes for complete saturation of the cells in an excess of hemagglutinin and occurred only in the absence of calcium ion. The amount of hemagglutinin required to saturate a given volume of red blood cells was also determined and the results correlated with the mechanism of the hemagglutination reaction. 3. 3. The antigenic relationship of the hemagglutinin to the virus elementary body was investigated. The antibody, reactive in the hemagglutination inhibition reaction, arose in response to an antigenic component present in the virus particle. This was determined by demonstrating the hemagglutinin inhibitor in the serum of roosters immunized with killed psittacosis virus. Spontaneous dissociation of the erythrocyte-hemagglutinin complex has not been observed, but the antibody contained in immune serum has the ability to disrupt an existing cell-hemagglutinin complex or otherwise to prevent the agglutination of cells. As a result of this observation, the hemagglutination inhibition test was modified by presaturating the murine red blood cells with hemagglutinin and adding these “sensitized” cells directly to serial dilutions of the test serum. The sensitivity of the hemagglutination reaction to low antibody titers was utilized in following the immune response of roosters to inoculation with the psittacosis virus. 4. 4. The chemical nature of the hemagglutinin was studied. The phospholipid lecithin and a nucleoprotein formed at least two of the most important components of the hemagglutinin. The possession of these chemical entities related the psittacosis virus hemagglutinin to the hemagglutinins of vaccinia and ectromelia viruses. Breakdown of the hemagglutinin nucleoprotein into its component amino acids and nucleic acid bases revealed its close relationship to a similar nucleoprotein constituent of the virus elementary body. Significance of this finding is discussed.