Abstract
Vaccination by intranasal (IN) inoculation with a replication-competent virus forms the basis of licensed and novel candidate respiratory viral vaccines (e.g., the cold-adapted influenza virus vaccine). A positive global impact of vaccination depends on vaccine efficacy in developing countries where dietary deficiencies are commonplace. The current study was designed using Sendai virus (SeV) as a model respiratory viral vaccine to test antibody-forming cell (AFC) residence and isotype expression in the context of a vitamin A deficiency (VAD). Samples were taken 1 mo after vaccination when AFCs generally reach their peak in healthy animals. In control animals on a healthy diet, SeV induced an antibody response with a relative bias toward IgA in the upper respiratory tract (URT, as sampled by nasal wash), and IgG in the lower respiratory tract (LRT, as sampled by bronchoalveolar lavage [BAL]). In the context of VAD, the SeV-specific IgA antibodies in the nasal wash were significantly reduced in favor of enhanced IgG antibodies in the BAL. When AFCs were examined in diffuse nasal-associated lymphoid tissues (d-NALT), lungs, cervical lymph nodes (CLN), and mediastinal lymph nodes (MLN), a similar pattern emerged. AFCs were most frequent in the d-NALT and most expressed IgA in control mice. In the context of VAD, these IgA-producing AFCs were significantly reduced in number, skewing the natural balance of IgA and IgG. Taken together, the results show that the VAD diet, which is well known for its association with immune defects in the gut, significantly alters AFC induction and isotype expression in the respiratory tract.