The Respiratory Tract Immune System in the Pig

The distribution of immunoglobulins A, G and M were assessed in the bronchial lymph node and palantine tonsil of pigs from birth to maturity, using the immunoperoxidase technique. Immunoglobulin-containing cells appeared earlier in the tonsil than in the lymph node; this probably reflects the exposure of the tonsil to environmental antigens. IgG-containing cells predominated after the first 3 weeks of life, but the IgA:IgG ratio was much higher in the tonsil than in the lymph node. Extracellular, reticular staining was visible in the central region of some follicles in addition to a few immunoglobulin-containing cells that resembled large lymphocytes or blast cells.