Abstract:
A standard radioactive chromium (51 Cr) release assay was used to assess the in vitro phagocytosis
and lysis of bovine erythrocytes by cultured splenic, bone marrow and peripheral blood monocytederived
(PBM) macrophages isolated from healthy and Trypanosoma congolense and T. vivax-infected
cattle of the Boran and N'Dama breeds.
Recombinant cytokines (rHuTNF-a and rBoIFN-y) and non-acid-dialysed peripheral blood mononuclear
cell (PBMNC) culture supernatants stimulated these PBM for enhanced activities. The stimulants
caused increases in the rate of erythrocyte phagocytosis and lysis by cultured PBM in a concentration-
dependent manner. But very high stimulant concentrations caused deceased in vitro
erythrophagocytosis. However, bacterial lipopolysaccharide (LPS) and acid-dialysed PBMNC culture
supernatants did not cause any increase in cultured PBM erythrophagocytosis.
In vitro erythrocyte phagocytosis and lysis by splenic, bone marrow and peripheral blood monocyte
(PBM)-derived macrophages of Boran breed of cattle infected with Trypanosoma congolense increased
from 14 days post-infection (DPI) onwards and thereafter maintained at various levels above pre-infection.
Cultured splenic macrophages showed the greatest erythrocyte destruction capability while
PBM-derived macrophages was the least. The rates of in vitro erythrocyte phagocytosis and lysis were
higher with the cultured PBM of the Beran than those of the N'Dama cattle during T. congolense infection
. The rate of in vitro erythrocyte destruction was however, similar in both groups of cattle during
T. vivax infection. These results correlated positively with the dynamics and degree of anaemia
developed by these groups of animals during both T. congolense and T. vivax infections.
Cattle infected with T. congolense and T. vivaxdeveloped varying degrees of normocytic normochromic
anaemia during infection. Boran cattle developed a more severe anaemia, and had to be treated
with diminazine aceturate, than N'Dama cattle during T. congolense infection. Both breeds of cattle
developed a milder but similar degree of anaemia during T. vivax infection. None of the animals were
treated.
The results of this study indicated a role of in vivo macrophage stimulatory factors, notably cytokines
such as TNF-a and IFN-r in host's serum, as well as parasite antigens, which may act singly or in
concert, in the process of enhanced erythrocyte destruction, hence anaemia by the mononuclear
phagocytic system (MPS) during bovine trypanosomosis.
