In Vitro Generation of Human High-Density-Lipoprotein-Resistant Trypanosoma brucei brucei

ABSTRACT The host range of African trypanosomes is influenced by innate protective molecules in the blood of primates. A subfraction of human high-density lipoprotein (HDL) containing apolipoprotein A-I, apolipoprotein L-I, and haptoglobin-related protein is toxic to Trypanosoma brucei brucei but not the human sleeping sickness parasite Trypanosoma brucei rhodesiense. It is thought that T. b. rhodesiense evolved from a T. b. brucei-like ancestor and expresses a defense protein that ablates the antitrypanosomal activity of human HDL. To directly investigate this possibility, we developed an in vitro selection to generate human HDL-resistant T. b. brucei. Here we show that conversion of T. b. brucei from human HDL sensitive to resistant correlates with changes in the expression of the variant surface glycoprotein (VSG) and abolished uptake of the cytotoxic human HDLs. Complete transcriptome analysis of the HDL-susceptible and -resistant trypanosomes confirmed that VSG switching had occurred but failed to reveal the expression of other genes specifically associated with human HDL resistance, including the serum resistance-associated gene (SRA) of T. b. rhodesiense. In addition, we found that while the original active expression site was still utilized, expression of three expression site-associated genes (ESAG) was altered in the HDL-resistant trypanosomes. These findings demonstrate that resistance to human HDLs can be acquired by T. b. brucei.

Download Full-text

Developmentally Regulated Sensitivity of Trypanosoma brucei brucei to the Cytotoxic Effects of Human High-Density Lipoprotein

Experimental Parasitology ◽

10.1006/expr.1995.1111 ◽

1995 ◽

Vol 81 (2) ◽

pp. 216-226 ◽

Cited By ~ 8

Author(s):

D.R. Moore ◽

A. Smith ◽

K.M. Hager ◽

R. Waldon ◽

J.D. Esko ◽

...

Keyword(s):

High Density Lipoprotein ◽

Trypanosoma Brucei ◽

Density Lipoprotein ◽

High Density ◽

Trypanosoma Brucei Brucei ◽

Developmentally Regulated ◽

Cytotoxic Effects ◽

Human High Density Lipoprotein

Download Full-text

The main lytic factor of Trypanosoma brucei brucei in normal human serum is not high density lipoprotein.

Journal of Experimental Medicine ◽

10.1084/jem.183.3.1023 ◽

1996 ◽

Vol 183 (3) ◽

pp. 1023-1029 ◽

Cited By ~ 58

Author(s):

J Raper ◽

V Nussenzweig ◽

S Tomlinson

Keyword(s):

High Density Lipoprotein ◽

Human Serum ◽

Trypanosoma Brucei ◽

Gel Filtration ◽

Density Lipoprotein ◽

High Density ◽

Lytic Activity ◽

Normal Human Serum ◽

Trypanosoma Brucei Brucei ◽

Normal Human

Natural immunity of humans to the cattle pathogen Trypanosoma brucei brucei has been attributed to the presence in normal human serum (NHS) of lytic factors for the parasites. We and others have shown that NHS contains two trypanolytic factors (herein termed TLF1 and TLF2) that can be separated by gel filtration. TLF1 copurifies with a subclass of high density lipoprotein (HDL), whereas TLF2 has a much higher molecular weight and does not appear to be a lipoprotein. We find that the trypanolytic activity of purified TLF1 is totally inhibited by exogenous haptoglobin (Hp) at concentrations (0.1 mg/ml) lower than those present in NHS (0.2-2 mg/ml). In contrast, exogenous Hp (up to 2.5 mg/ml) has no effect on the lytic activity of either NHS or isolated TLF2. Hp-depleted sera from patients with intravascular hemolysis is severalfold more trypanolytic than NHS. These sera contain only TLF1, and their lytic activity is totally abolished upon the addition of Hp (0.1 mg/ml). When NHS containing different Hp allotypes is fractionated by gel filtration, TLF1 activity is either revealed or remains masked, depending on whether it coelutes with Hp. Masked TLF1 activity in the column fractions is revealed if Hp is removed by density gradient ultracentrifugation. We conclude that endogenous Hp inhibits TLF1 activity, and that TLF2 is the main trypanolytic factor in NHS.

Download Full-text

Endocytosis of a cytotoxic human high density lipoprotein results in disruption of acidic intracellular vesicles and subsequent killing of African trypanosomes.

The Journal of Cell Biology ◽

10.1083/jcb.126.1.155 ◽

1994 ◽

Vol 126 (1) ◽

pp. 155-167 ◽

Cited By ~ 103

Author(s):

K M Hager ◽

M A Pierce ◽

D R Moore ◽

E M Tytler ◽

J D Esko ◽

...

Keyword(s):

High Density Lipoprotein ◽

Human Serum ◽

Density Lipoprotein ◽

High Density ◽

Surface Binding ◽

African Trypanosomes ◽

Trypanosome Lytic Factor ◽

Human High Density Lipoprotein ◽

A Minor ◽

Endocytic Vesicles

The host range of Trypanosoma brucei brucei is restricted by the cytolytic effects of human serum high-density lipoprotein (HDL). The lytic activity is caused by a minor subclass of human serum HDL called trypanosome lytic factor (TLF). TLF binds in the flagellar pocket to specific TLF-binding sites. Internalization and localization of TLF to a population of endocytic vesicles, and ultimately large lysosome-like vesicles, precedes lysis of T. b. brucei. The membranes of these large vesicles are disrupted by the accumulation of TLF particles. Inhibitor studies with lysosomotropic amines have shown these large vesicles to be acidic in nature and that prevention of their rupture spares the cells from TLF-mediated lysis. Furthermore, leupeptin inhibition suggests that a thioprotease may be involved in the mechanism of TLF-mediated lysis of T. b. brucei. Based on these results, we propose a lytic mechanism involving cell surface binding, endocytosis and lysosomal targeting. This is followed by lysosomal disruption and subsequent autodigestion of the cell.

Download Full-text