[5] It acts as a molecule of innate immunity in association with apolipoprotein L1 (ApoL 1)-containing high-density lipoprotein (HDL) particles.

[6] In humans, together with related serum protein, haptoglobin, it acts as a cell-killing agent as part of the trypanolytic factor against the protozoan parasite Trypanosoma brucei thereby providing natural resistance to African sleeping sickness.

[15] As they reported: "Southern blot analysis provides evidence for the presence of more than one haptoglobin gene per haploid genome and confirms that there is restriction site polymorphism at this locus.

[17] The protein, Hpr, was determined by New York University Medical Center scientists Madhavi Muranjan, Victor Nussenzweig and Stephen Tomlinson in 1998.

[18][22] The major function of Hpr is protection from infection with Trypanosoma brucei to provide natural resistance to African sleeping sickness.

[7] Together with haptolglobin and apoliproproteins, it makes up a trypanolytic factor TLF 1 in the blood of primates that can kill invading the animal strain of T. brucei (specifically T. b.

[24] The human strains, T. b. rhodesiense and T. b. gambiense have acquired resistance to TLF indicating an evolutionary arms race between primates and the protozoan parasite.