Inflammation can be treated or prevented altogether by administering a preparation comprising IgA. These preparations also can effect immunomodulation. Preferably, the preparation includes multimeric IgA and is essentially free of IgG in its various forms. Other compounds, such as antibiotics, antiphlogistic agents and antacids, also may be administered. Immunoglobulin A may also be used in vaccines to prevent inflammation. Additionally, an improved assay for evaluating anti-inflammatory activity is provided.