FIG 1.

Occurrence of T4 phage neutralizing antibodies in human population. (A) Phage inactivation by human sera. Bacteriophage T4 (10⁶ PFU/ml) was incubated for 2 h with human sera (50 healthy volunteers); after that, phage viability was tested on bacteria by the double-layer method. Results were compared to the phage titer control and classified into two groups. Negative sera were those not inactivating the phage (phage titer after incubation was within the range of the mean value of the control ± 2 SDs); nine samples could be classified into this group. Positive sera were those inactivating the phage (phage titer after incubation was lower than the range of the negative samples); 41 samples were classified into this group. Control was calculated from titers of the same phage preparation incubated with sera of nonimmunized SPF standard mice (n = 8, mean = 0.955 × 10⁶ PFU/ml, SD = 0.159 × 10⁶ PFU/ml). *, phage titer after incubation with phage-inactivating (positive) sera was significantly decreased in comparison to phage titer after incubation with the noninactivating (negative) sera (P = 0.00002) and in comparison to the titer control (P = 0.00001; Kruskal-Wallis ANOVA). Whiskers represent minimal and maximum readouts, boxes represent SD, and medians are marked by bars. (B) Natural IgG antibodies specific to T4 head surface proteins in human population. Reverse cumulative distribution plots for each head protein (gp23*, gp24*, Hoc, and Soc) were assigned to the human sera, according to the work of Miura et al. (28). Cutoff values for nonimmunized individuals are represented by vertical lines in each plot. Comparison of the plots and statistical analysis show that immunization to gp23* markedly prevails in the human population (P < 0.00001; Kruskal-Wallis ANOVA).