Human T-cell leukemia virus type I (HTLV-I) is a retrovirus that causes adult T-cell leukemia. The male-to-female transmission is stronger than the reverse, so the carrier proportion of women is greater than that of men. On the other hand, since the mother-to-child transmission route via the breast-feeding is common for baby boys and girls, it has been thought the HTLV-I proportions of boys and girls are the same until now. A question arises as to whether the "innate protection powers against human virus" are the same between baby boys and girls. We utilize Blood donors in 1995-1998, which were provided by Japan Red Cross Society of Oita, Japan. The data are summarized into the frequency table with respect to gender and age. The age groups are <20, 20<age≤30, 30<age≤40, 40<age≤50, and >50 years old. The comparison of carrier proportions of males and females under 20 years old is made with a two-sided statistical test and for the other groups one-sided tests are carried out. The preset statistical analysis shows that the carrier proportion of girls is less than that that of boys. It implies that in HTLV-I the mother-to-child transmission probability of females is less than that of males. According to the present findings, it follows that the female's innate protection power against HTLV-I is stronger than that of males, and the conclusion may become a valid proposition for general human virus
