Infection drives localised and individualised antibody repertoires, whereas immunisation promotes repertoire convergence in pig

Respiratory viruses elicit mucosal and systemic immunity, yet how tissue compartmentalisation and exposure route shape B cell repertoires remain unclear. Using the pig model, we characterised antibody repertoires in bronchoalveolar lavage, tracheobronchial lymph nodes, spleen, and blood following intranasal infection with pandemic influenza virus (pH1N1) or porcine respiratory coronavirus (PRCV), and after intramuscular PRCV immunisation. Infection induced highly compartmentalised responses, with antigen-associated clones enriched in lung, lymph nodes and spleen but with limited presentation in blood. These clones were largely private, indicating individualised responses, and displayed tissue-specific diversity. The similar tissue distributions between pH1N1 and PRCV infections suggest a conserved spatial organisation, although differential lymph node involvement indicates pathogen-specific effects. In contrast, intramuscular immunisation generated more convergent, public repertoires in blood, characterised by reduced clonal size diversity. Monoclonal antibody analysis revealed functional heterogeneity and limited overlap with bulk repertoires. Together, these findings show that despite stable germline usage, functional antibody responses are shaped by the route of antigen exposure, clonal selection, and host specific factors, resulting in distinct repertoire architectures between infection and immunisation. Author summaryRespiratory viruses such as influenza and coronaviruses infect the airways and lungs, where they trigger immune responses that help the body fight infection. Most studies of immunity rely on blood, although many immune cells function in tissues like the lungs. Therefore, we may be missing important parts of the immune response. We used pigs, a large animal model that closely resembles humans in respiratory biology and is naturally infected with influenzas and coronaviruses, to investigate how immune responses are shaped by infection compared with intramuscular vaccination. We examined B cells in lungs, nearby lymph nodes, spleen, and blood after infection with influenza or a porcine coronavirus and compared these with responses after vaccination. We found that infection generates distinct, individual immune responses in the lung and lymphoid organs. Vaccination by injection led to more similar responses across animals, mostly in the blood. This suggests the way the immune system encounters an antigen influences the response generated. We also showed that antibodies with similar binding properties can behave very differently in their ability to neutralise viruses. Our findings show that infection and vaccination shape immunity in fundamentally different ways, with important implications for designing vaccines that better protect against respiratory diseases.