Human coronavirus NL63 and 229E seroconversion in children

Abstract

In 2004, the novel respiratory human coronavirus NL63 (HCoV-NL63) was identified, and subsequent research revealed that the virus has spread worldwide. HCoV-229E is a close relative of HCoV-NL63, and infection with either virus can lead to the hospitalization of young children, immunocompromised persons, and the elderly. Children infected with HCoV-NL63 often develop croup, with obstruction of the airway. In this study we investigated at which age children are confronted for the first time with an HCoV-NL63 infection and, thus, at which age they seroconvert to HCoV-NL63 positivity. We designed a recombinant HCoV-229E and a recombinant HCoV-NL63 nucleocapsid protein enzyme-linked immunosorbent assay and performed a seroepidemiology survey on longitudinal and cross-sectional serum samples. The longitudinal serum samples were collected from 13 newborns, and data for those newborns were available from multiple time points spanning a period of at least 18 months. For the cross-sectional survey we tested serum samples of 139 children, including newborns to children 16 years of age. In examinations of the longitudinal serum samples we observed that all of the children had maternal anti-NL63 and anti-229E antibodies at birth that disappeared within 3 months. Seven of the 13 children became HCoV-NL63 seropositive during follow-up, whereas only 2 became HCoV-229E seropositive. The serology data of the cross-sectional serum samples revealed that 75% and 65% of the children in the age group 2.5 to 3.5 years were HCoV-NL63 and HCoV-229E seropositive, respectively. We conclude that on average, HCoV-NL63 and HCoV-229E seroconversion occurs before children reach the age of 3.5 years.

FIG. 1.

Lack of cross-reactivity between antibodies directed to HCoV-NL63 N protein and those directed to HCoV-229E N protein. Serum of an adult known to be positive for HCoV-NL63 and HCoV-229E was diluted (1:200) and preincubated with serial dilutions of proteins. (A) Competition between soluble HCoV-NL63 N protein (closed triangles, continuous line), HCoV-229E N protein (open squares, dashed line), and LacZ protein (open circles, continuous line) in an HCoV-NL63 N protein ELISA. (B) Competition between soluble HCoV-NL63 N protein (closed triangles, continuous line), HCoV-229E N protein (open squares, dashed line), and LacZ protein (open circles, continuous line) in an HCoV-229E N protein ELISA. RLU, relative luminescence units.

FIG. 2.

HCoV-NL63 and HCoV-229E N protein-directed antibody levels in follow-up serum samples from 13 children. Each graph (A through M) represents the longitudinal profiles of levels of HCoV-NL63 N protein (closed triangles, continuous line)- and HCoV-229E N protein (open squares, dashed line)-directed antibody for a single child. The measured antibody levels are indicated as relative luminescence units (10⁶) on the y axis. The follow-up period is plotted on the x axis.

FIG. 3.

Cumulative levels of incidence of HCoV-NL63 and HCoV-229E infections. The Kaplan-Meier survival analysis was performed using values representing the cumulative levels of incidence of the percentages of seronegative individuals (y axis) plotted against time (in months; x axis). Seroconversion to HCoV-NL63 positivity is presented as a continuous line; seroconversion to HCoV-229E positivity is presented as a dashed line. The time point of seroconversion was calculated by taking the midpoint between the last seronegative and the first seropositive time points.

FIG. 4.

Percentages of HCoV-NL63- and HCoV-229E-seropositive results in different age groups. The percentages of HCoV-NL63 (black bars)- and HCoV-229E (gray bars)-seropositive individuals were monitored using serum samples obtained from children of various ages. m, months, y, years.