EFFECT OF HAPTOGLOBIN PHENOTYPES ON GROWTH OF STREPTOCOCCUS-PYOGENES

The haptoglobin (Hp) 2-1 and 2-2 phenotypes have been shown to aggluti nate Streptococcus pyogenes carrying the membrane antigen T4. In this study, the growth rate of two strains of Streptococcus pyogenes (T1 an d T4) in human serum was compared among haptoglobin phenotypes in vitr o. During incubation for 16 hours in serum of different haptoglobin ty pes, only Hp 2-1 and Hp 2-2 sera showed an inhibitory effect on growth , Hp 2-2 being 1.85 times more potent than Hp 2-1. Growth of Streptoco ccus pyogenes T4 negatively correlated with the serum concentration of Hp 2-1 (r = - 0.908) and Hp 2-2 (r = - 0.953). Haptoglobin-depleted s erum had no inhibitory effect on bacterial growth. Addition of haemogl obin and ferric citrate to the serum accelerated the growth of Strepto coccus pyogenes T4 (P < 0.05) but not in Hp 2-2 serum. Haptoglobin typ es 2-1 and 2-2 can be regarded as inhibitors of Streptococcus pyogenes growth in vitro. These data point towards a potential protective role of Hp 2-2 in Streptococcus pyogenes infection in vivo, independently of iron uptake.