Journal of Lipid Research, Vol 33, 1639-1646, Copyright © 1992 by Lipid Research, Inc.
Transgenic mice expressing human apolipoprotein A-I have sera with modest trypanolytic activity in vitro but remain susceptible to infection by Trypanosoma brucei brucei
JS Owen, MP Gillett and TE Hughes
University Department of Medicine, Royal Free Hospital School of Medicine (University of London), England.
Although Trypanosoma brucei brucei fatally infects livestock in much of
sub-Saharan Africa, humans are innately resistant to infection, apparently
because high-density lipoproteins (HDL) in human serum lyse this
unicellular protozoan parasite. Recently, we demonstrated that purified
human apolipoprotein (apo) A-I, the major protein (M(r) 28,016) constituent
of HDL, had full trypanolytic activity in vitro whereas the apoA-I of
cattle and sheep was non-lytic. In the present study, we have sought to
confirm the trypanocidal capability of human apoA-I by studying four lines
of transgenic mice expressing (supra)physiological serum levels of this
polypeptide. Although trypanolysis in vitro by sera from transgenic mice
(15.1 +/- 1.3% [mean +/- SEM], n = 30) was considerably less than by human
sera (typically 60-80%), it was nevertheless significantly greater than by
control sera (8.5 +/- 1.1%, n = 10; P < 0.001) and correlated with the
concentration of human apoA-I (r = 0.56, P < 0.001). When trypanosomes
were incubated at 37 degrees C with human serum or with human apoA-I for 30
min (i.e., within the pre-lytic period) they lost their ability to
subsequently infect mice; trypanosomes incubated with transgenic mice serum
remained infective. Furthermore, transgenic mice were fully susceptible to
infection when inoculated with 10(3) trypanosomes; both the initial
detection of trypanosomes in the blood (3-4 days) and the time to death
(5-6 days) were no longer than control mice. This apparent paradox between
the action of human apoA-I in human serum and in mouse serum was
investigated further.(ABSTRACT TRUNCATED AT 250 WORDS)