Sickled red cells in the Cervidae

Hemoglobin polymerizes within the red cells from most species of deer when exposed to oxygen and an elevated pH. This hemoglobin aggregation is related to specific beta chains, which also dictate the precise alignment of the molecules and the type of cellular distortion. The typical sickle cell is virtually identical in shape, mechanical fragility, and viscosity to the human sickle cell, whereas the matchstick cell shares the latter properties but is an elongate cell from which spicules protrude in only one direction. The conditions of pH and pO2 that are required are beyond the usual physiological ranges; therefore, neither in vivo sickling nor disease is seen in deer. The genetic makeup of deer hemoglobin is of interest because of duplication of the alpha-chain gene loci and because of an extreme variability of the primary structure of the beta chains, at least in the white-tailed deer. Many facets of the deer hemoglobins remain fascinating objects for speculation. The evolutionary significance, if any, of the almost universal presence of sickling in the Cervidae is unknown. The meaning of the extreme polymorphism of the deer hemoglobins and the mechanisms by which they occurred are also obscure. It may be, however, that they may provide a tool by which one can elucidate the contact points and bonds that lead to the polymerization that produces the picturesque sickle cell.