Blood and Tissue Leukocyte Apoptosis in Trypanosoma brucei Infected Rats

Severity of disease in human African trypanosomiasis may be linked, as in other human protozoan infections, to apoptosis of host inflammatory cells during infection. The present study investigates the involvement of leukocyte apoptosis in Trypanosoma brucei infection of rodents. Twenty-seven Wistar rats were infected with 1 × 103 T. brucei and leukocyte apoptosis was evaluated by several methods. Apoptotic cell count was performed in blood, spleen, thymus, lymph node and liver during infections, using Light Microscopy (LM), agarose gel electrophoresis and Transmission Electron Microscopy (TEM). Blood and tissues leukocyte apoptosis in infected animals were confirmed by LM, TEM, and agarose gel electrophoresis, which showed low molecular weight DNA fragments. Infected rats sacrificed after day 8 PI showed significant increase in apoptotic cells in both blood (p < 0.001) and spleen (p < 0.05). Peak blood leukocyte apoptosis corresponded with peak parasitemia and the lowest total leukocyte count in all infected rats. Our data provide the first documentation of increased levels of blood leukocyte apoptosis during T. brucei infection. Apoptosis of blood cells during trypanosome infection may represent a putative mechanism for the severity of leukopenia and disease.