The accumulation of immunoglobulin (Ig)A antibody-secreting cells (ASCs) in the lactating mammary gland leads to secretion of antibodies into milk and their passive transfer to the suckling newborn. This transfer of IgA from mother to infant provides transient immune protection against a variety of gastrointestinal pathogens. Here we show that the mucosal epithelial chemokine CCL28 is up-regulated in the mammary gland during lactation and that IgA ASCs from this tissue express CCR10 and migrate to CCL28. In vivo treatment with anti-CCL28 antibody blocks IgA ASC accumulation in the mammary gland, inhibiting IgA antibody secretion into milk and the subsequent appearance of antibody in the gastrointestinal tract of nursing neonates. We propose that CCL28 is a key regulator of IgA ASC accumulation in the mammary gland and thus controls the passive transfer of IgA antibodies from mother to infant.