1)The serological responses of 29 cases of human yellow fever infection were studied by hemagglutination-inhibition (HI), complement-fixation (CF) and neutralization (N) tests.
2)The cases were divided into two groups, chiefly according to the pattern of CF antibodies to a variety of Group B agents. The 17 cases in the first group are considered to be primary infections of yellow fever; the 12 cases in the second are considered to be infections of yellow fever in individuals who had previously been infected with another Group B virus.
3)In primary infections of yellow fever specific HI antibodies appear first, followed rapidly by antibodies to other Group B viruses. The titers of homologous HI antibodies are always as high as, or higher than, the titers of heterologous antibodies.
4)In primary infections there is great variation in the time after onset at which CF antibodies become demonstrable. Complement-fixing antibodies are produced over a long period and may still be increasing when HI antibodies are diminishing. The pattern of CF antibodies is remarkably specific. Overlaps with other antigens occur only when the homologous CF antibodies are high.
5)In primary infections the development of N antibodies as determined by the standard intracerebral test is quite specific. Heterologous N antibodies are developed to a limited extent.
6)In cases of secondary infection, the production of HI and CF antibodies is both massive and very rapid. There is no suggestion of specificity in the patterns developed and, in fact, as a rule the highest HI and CF antibodies were heterologous. Furthermore, in secondary infections the production of heterologous N antibodies is stimulated to a greater extent than in primary infections. In the present 12 cases, the heterologous response was so great that in all but one of the cases accurate diagnosis of the current illness by N test was impossible.