Comparison of enterovirus-specific cellular immunity in two populations of young children vaccinated with inactivated or live poliovirus vaccines

Abstract

Enterovirus-specific cellular immunity was studied in Estonian and in Finnish children at the age of 9 months. The aim was to evaluate the level of responsiveness in two neighbouring countries with different poliovirus immunization practices and striking differences in the incidence of insulin-dependent diabetes mellitus (IDDM), a disease in which early enterovirus infections are an aetiological risk factor. The Estonian children immunized with live attenuated polio vaccine had stronger T cell responses to coxsackievirus B4 and poliovirus type 1 when compared with Finnish children immunized with inactivated polio vaccine (median stimulation indices 10.4 and 6.3 in Estonian children and 1.9 and 2.9 in Finnish children, respectively; P < 0.05). Lymphocytes stimulated by poliovirus type 1 antigen expressed interferon-gamma (IFN-gamma) mRNAs, which strongly correlated with the level of proliferation responses. Lymphocytes of Estonian children had a tendency towards stronger expression of IFN-gamma upon poliovirus challenge when compared with Finnish children. The number of children who had experienced coxsackievirus B infections, as determined by the presence of neutralizing antibodies, did not differ between Estonian and Finnish children. The results show that Finnish children have weaker cellular immunity against enteroviruses at the age of 9 months compared with Estonian children at the same age. This is most probably due to the difference in polio vaccination schedules; in Estonia live poliovirus vaccine is used and given at earlier ages than the inactivated vaccines in Finland. This leads to stronger T cell immunity which cross-reacts with other enterovirus serotypes. This may explain the lower incidence of IDDM in Estonia by providing effective protection against diabetogenic enterovirus strains in Estonian children.

Fig. 1

T cell responses to tetanus toxoid (TT), poliovirus type 1, coxsackievirus B4 and adenovirus hexon protein in Estonian children (□) and Finnish children (hatched). The horizontal line in the box shows the median value. The outlines of the boxes show the 25% and 75% percentiles, while the bars outside the boxes represent the 10% and 90% percentiles. ○, Values outside this range. P values for the differences between the stimulation index (SI) values were calculated using the Mann–Whitney U-test.

Fig. 2

Correlation between the T cell responses (in stimulation index (SI) values) to poliovirus type 1 and coxsackievirus B4 in the Estonian and Finnish children.

Fig. 3

Correlation between lymphocyte proliferation and IFN-γ mRNA expression of poliovirus type 1 antigen-stimulated peripheral blood mononuclear cells (PBMC). Both Estonian and Finnish children are included. s/n, Signal to noise values.