Abstract Background The incidence of community-acquired pneumonia and lower respiratory tract infection rises considerably in later life. Immunoglobulin M (IgM) antibody levels to pneumococcal capsular polysaccharide are known to decrease with age; however, whether levels of IgM antibody to pneumococcal proteins are subject to the same decline has not yet been investigated. Methods This study measured serum levels and binding capacity of IgM antibody specific to the pneumococcal surface protein A (PspA) and an unencapsulated pneumococcal strain in serum isolated from hospital patients aged