# The Complexity of Immunoglobulin A Immune Responses in Respiratory Syncytial Virus Infection

## TL;DR

This paper reviews how infants have weaker IgA immune responses to RSV compared to adults, and how regulatory B cells may play a role in this, affecting vaccine development.

## Contribution

The paper highlights the role of neonatal regulatory B cells in suppressing IgA responses during RSV infection in infants.

## Key findings

- Infants mount weaker IgA responses to RSV compared to adults.
- Regulatory B cells, especially neonatal Bregs, suppress antiviral immunity and contribute to severe RSV disease.
- Understanding IgA regulation could improve infant vaccine design.

## Abstract

Respiratory syncytial virus (RSV) remains a leading cause of severe lower respiratory tract disease in infants worldwide. Despite extensive study in animal models and humans, fundamental age-dependent differences in mucosal immunity continue to limit the development of durable protective strategies in early life. Compared to adults, infants mount weaker humoral responses to RSV, underscoring the urgent need for effective vaccines in this age group. Immunoglobulin A (IgA), the dominant antibody isotype at respiratory mucosal surfaces, plays a central role in limiting viral replication and disease severity during RSV infection. While IgA limits RSV severity in adults, infants fail to generate robust IgA responses. Impaired IgA responses in infancy reflect unique immune regulatory pathways that shape early-life antiviral immunity. Emerging evidence highlights a critical role for regulatory B cells (Bregs), particularly neonatal Bregs (nBregs), in suppressing antiviral responses, limiting class switch recombination, and contributing to severe RSV disease. This review summarizes current evidence on IgA regulation during RSV infection, with particular emphasis on age-specific B-cell responses and the emerging role of Bregs. Improved understanding of these mechanisms has direct implications for the rational design of vaccines and immunomodulatory strategies tailored to infants.