Immune responses to SARS-CoV-2 in three children of parents with symptomatic COVID-19

Abstract

Compared to adults, children with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have predominantly mild or asymptomatic infections, but the underlying immunological differences remain unclear. Here, we describe clinical features, virology, longitudinal cellular, and cytokine immune profile, SARS-CoV-2-specific serology and salivary antibody responses in a family of two parents with PCR-confirmed symptomatic SARS-CoV-2 infection and their three children, who tested repeatedly SARS-CoV-2 PCR negative. Cellular immune profiles and cytokine responses of all children are similar to their parents at all timepoints. All family members have salivary anti-SARS-CoV-2 antibodies detected, predominantly IgA, that coincide with symptom resolution in 3 of 4 symptomatic members. Plasma from both parents and one child have IgG antibody against the S1 protein and virus-neutralizing activity detected. Using a systems serology approach, we demonstrate higher levels of SARS-CoV-2-specific antibody features of these family members compared to healthy controls. These data indicate that children can mount an immune response to SARS-CoV-2 without virological confirmation of infection, raising the possibility that immunity in children can prevent the establishment of SARS-CoV-2 infection. Relying on routine virological and serological testing may not identify exposed children, with implications for epidemiological and clinical studies across the life-span.

Fig. 1. Timeline of travel, exposure, symptoms, and selected results.

Nasopharyngeal PCR, saliva, and serum antibodies are shown for each parent and child. Key events in the timeline are highlighted according to anumber of days following the return of parents to the household.

Fig. 2. Longitudinal cellular immune profiling in parents and children.

a Major immune cell populations in PBMC at day 12, 37, and 88 in parents (solid line) and children (broken line) (A1 (closed circles), A2 (closed squares), C1 (open circles), C2 (open squares), C3 (open triangles)). b tSNE dimensionality reduction of immune cell populations in all PBMC samples across the three-time points. The tSNE plot was generated from a concatenated file containing 300,000 events (20,000 randomly selected live single cells per patient per time point). c. Frequency of monocyte subpopulations in PBMC from parents and children. d Frequency of CD8 T cell naive, effector, and memory subpopulations in PBMC. e Frequency of PD1 expressing CD8 T cells over time. f Frequency of CD4 T cell naive, effector, and memory subpopulations in PBMC. g tSNE dimensionality reduction of whole blood samples. The tSNE plot was generated from a concatenated file containing 300,000 events (20,000 randomly selected live single cells per patient per time point). Coloring depicts SSC and CD16 expression in tSNE islands. Granulocyte populations (neutrophils and eosinophils) are expressed as the proportion of leukocytes. h Frequency of low-density CD16⁺SSC^hi neutrophils (CD14⁺ and CD14⁻) in PBMC fraction at day 88. i Plasma cytokine concentration of three detectable cytokines, RANTES (blue), MCP-1 (purple), and IL-8 (green) in children and parents at day 12 and 37.

Fig. 3. Salivary and plasma antibody responses against SARS-CoV-2 S1 protein by ELISA and by microneutralization assay.

a Anti-S1 salivary IgA, IgG, and IgM. # IgA anti-S1 response that developed concurrent with resolution of symptoms. b Anti-S1 plasma IgA, IgG, and IgM. c Neutralizing antibody activity in plasma. A1: mother, A2: father, C1: male (9 years), C2: male (7 years), C3: female (5 years), (P) positive control.

Fig. 4. Family of symptomatic SARS-CoV-2 PCR positive parents and SARS-CoV-2 PCR negative children have distinct serological responses compared to healthy individuals, characterized by elevated SARS-CoV-2 specific responses.

a PLSDA scores plot of healthy (blue triangles) vs family (circles) containing both SARS-CoV-2 PCR positive parents (orange) and negative children (yellow) exhibited 98.0% calibration and 96.0% cross-validation accuracy, with 62.7% of variance explained by LV1 (x-axis). Family member samples are labeled with A (adult) or C (child) with the day of sample collection listed after D. b PLSDA plot of LV1 loadings driving the separation of groups, where negatively loaded features are associated with the family members. c Hierarchical clustering of healthy individuals (blue) and family members (parents, orange; children, yellow) using a feature-selected serological signature, where red indicates a relatively high antibody response and blue a relatively low antibody response (z-score). Samples (x-axis) are labeled with H (healthy non-household members), and A (adult) or C (child). Day of sample collection is listed at the end of family member sample labels.