Experimental infection with the respiratory Gram negative pathogen Actinobacillus pleuropneumoniae also caused a decrease in pig AGP serum concentrations, concomitantly with an increase in haptoglobin (Fig. 4C and (33)), dropping from around 0.8 mg/ml to 0.6 mg/ml at day 2 p.i. With the Gram positive pathogen Staphylococcus aureus (Fig. 4D) a 3–5 fold increase in haptoglobin at 30–48 hours after challenge was accompanied by a small decrease in pig AGP, going from a mean in 5 animals around 1.1 mg/ml to 0.7 mg/ml, however with a big animal to animal variation. The gene discussed is HP; the disease is infection.