Using an improved phagocytosis assay to evaluate the effect of HIV on specific antibodies to pregnancy-associated malaria.
BACKGROUND
Pregnant women residing in malaria endemic areas are highly susceptible to Plasmodium falciparum malaria, particularly during their first pregnancy, resulting in low birth weight babies and maternal anaemia. This susceptibility is associated with placental sequestration of parasitised red blood cells expressing pregnancy-specific variant surface antigens. Acquisition of antibodies against these variant surface antigens may protect women and their offspring. Functions of such antibodies may include prevention of placental sequestration or opsonisation of parasitised cells for phagocytic clearance.


RESULTS
Here we report the development and optimisation of a new high-throughput flow cytometry-based phagocytosis assay using undifferentiated Thp-1 cells to quantitate the amount of opsonizing antibody in patient sera, and apply this assay to measure the impact of HIV on the levels of antibodies to a pregnancy malaria-associated parasite line in a cohort of Malawian primigravid women. The assay showed high reproducibility, with inter-experimental correlation of r(2) = 0.99. In primigravid women, concurrent malaria infection was associated with significantly increased antibodies, whereas HIV decreased the ability to acquire opsonising antibodies (Mann-Whitney ranksum: p = 0.013). This decrease was correlated with HIV-induced immunosuppression, with women with less than 350 x 10(6) CD4+ T- cells/L having less opsonising antibodies (coef: -11.95,P = 0.002). Levels of antibodies were not associated with protection from low birth weight or anaemia.


CONCLUSIONS
This flow cytometry-based phagocytosis assay proved to be efficient and accurate for the measurement of Fc-receptor mediated phagocytosis-inducing antibodies in large cohorts. HIV was found to affect mainly the acquisition of antibodies to pregnancy-specific malaria in primigravidae. Further studies of the relationship between opsonising antibodies to malaria in pregnancy and HIV are indicated.
Department of Medicine, University of Melbourne, Post Office Royal Melbourne Hospital, Melbourne, Victoria, Australia.
Ricardo
R
Ataíde
Wina
W
Hasang
Danny W
DW
Wilson
James G
JG
Beeson
Victor
V
Mwapasa
Malcolm E
ME
Molyneux
Steven R
SR
Meshnick
Stephen J
SJ
Rogerson
D000740:Anemia / Q000150:complications / Q000276:immunology; D000913:Antibodies, Protozoan / Q000276:immunology*; D000918:Antibody Specificity / Q000276:immunology*; D000953:Antigens, Protozoan / Q000276:immunology; D002454:Cell Differentiation; D002460:Cell Line; D015331:Cohort Studies; D005260:Female; D006678:HIV / Q000276:immunology*; D015658:HIV Infections / Q000150:complications / Q000276:immunology / Q000469:parasitology; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007074:Immunoglobulin G / Q000276:immunology; D007230:Infant, Low Birth Weight / Q000276:immunology; D007231:Infant, Newborn; D016778:Malaria, Falciparum / Q000150:complications / Q000276:immunology* / Q000473:pathology; D010587:Phagocytosis / Q000276:immunology*; D011247:Pregnancy; D015597:Pregnancy Complications, Parasitic / Q000276:immunology*
D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D006454:Hemoglobins; D007074:Immunoglobulin G