MHC allele 242 suppresses the <i>H. majoris</i> infection in both young and old birds.

<p><i>H. majoris</i> infection intensity (ln(parasite infection intensity+1)) in blue tits, aged 2Y (open circles) or 3Y+ (filled circles), that carry or do not carry the MHC-I allele 242 (mean±2SE). Allele 242 suppresses the <i>H. majoris</i> infection in all birds although young birds (2Y) have higher infection intensities.</p