After TGEV challenge (PCD 4), the numbers of IgG-ASC and to a lesser extent IgA-ASC increased rapidly in the intestinal lamina propria of the PRCV-exposed pigs, suggesting that virus-specific IgG-ASC precursors derived in BALT or systemic lymphoid tissues of the PRCV-exposed pigs may migrate to the intestine in response to TGEV challenge and contribute to the partial protection observed.