MBP and infection: Effects of infection and its interaction with housing on changes in antibody titers after infection After infection with PRRSV, there was no housing or infection effect on MBP-IgG, but after infection with A. pleuropneumoniae, there was a housing effect on MBP-IgG (F(1.50) = 11.6, P < 0.01), with higher titers in barren than in enriched housed pigs (Figure 2D).