In many respects, our understanding of innate immune responses to protozoan parasites still lags behind that for other infectious organisms. However, recent work has shown that an important part of the armory against African trypanosomes is serum apolipoprotein L-I (apoL1), which can kill the parasite by causing lysis—why, then, would the parasites take it in? Vanhollebeke et al. show that apoL1 is taken up by the parasite via a specific glycoprotein receptor, which the parasite normally uses to supply heme for its growth and resistance to oxidative stress within the host. In human serum, however, the receptor also inadvertently recognizes a component of certain high-density lipoprotein complexes, of which apoL1 is a part, explaining how the uptake of this detrimental host protein is triggered.
B. Vanhollebeke, G. De Muylder, M. J. Nielsen, A. Pays, P. Tebabi, M. Dieu, M. Raes, S. K. Moestrup, E. Pays, A haptoglobin-hemoglobin receptor conveys innate immunity to Trypanosoma brucei in humans. Science 320, 677-681 (2008). [Abstract] [Full Text]