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The antigenicity of five strains of E. histolytica capable of multiplying at 25°C or lower, as well as at 35°C, was compared with that of eight strains of classic E. histolytica. All strains were grown at 35°C and were exposed to the same dilution of a single fluorescent anti-E. histolytica serum mixed with nonfluorescent normal or anti-E. histolytica sera. Fluorescence was measured with a microfluorimeter. Both groups showed a spectrum of fluorescent brightnesses for their component strains, but the average was 36.2 for body-temperature strains and only 21.2 for the reduced-temperature group. Clear distinction, without overlap between the two groups, occurred in inhibition reactions with a single unlabeled antiserum.
Three lines from a single strain of body-temperature amebae, cultured separately for several years under different conditions and tested after 1½ to 9 months under the same cultural conditions, showed significant differences in brightness. However, the inhibition pattern for all three strains was comparable to that of the other body-temperature amebae.
Reactions of a single strain of E. moshkovskii were indistinguishable from those of reduced-temperature E. histolytica. On the other hand, a strain of E. coli was clearly different from any of the E. histolytica strains on the basis of its inhibition pattern.
None of the reduced-temperature E. histolytica and neither E. moshkovskii nor E. coli were infective to guinea pigs. Six out of nine cultures of body-temperature E. histolytica infected guinea pigs, causing mild to extensive pathologic changes in the cecum. The other three strains were noninfective.
Present address: Bionetics Research Laboratories, Kensington, Maryland 20795.
Present address: Walter Reed Army Institute of Research, Washington, D. C. 20012.