Chemokine modulation in microscopic and submicroscopic Plasmodium falciparum malaria infection in women at delivery in Yaounde, Cameroon

In pregnancy-associated malaria, chemokines such as CXCL-4, CXCL-13, CXCL-16, and CCL-24 play critical roles in leucocyte trafficking to tissue sites in the infected placenta where inflammatory reactions are active. However, how plasma levels of these chemokines associate with Plasmodium falciparum placental malaria and pregnancy outcomes remains not well understood. The present study analyzed the plasma levels of CXCL-4, CXCL-13, CXCL-16, and CCL-24 chemokines in matched peripheral, placental and cord blood in relation with placental malaria (PM), and with submicroscopic parasitaemia. This was a retrospective case-control study (1:3 ratio) involving samples from 134 women (34 PM+ and 100 PM-) enrolled at delivery at the Marie Reine Health Center in Yaounde, Cameroon between June 2013 and October 2018. Samples were collected just after delivery and used to diagnose microscopic and submicroscopic Plasmodium falciparum infections. Submicroscopic infections were detected by reverse transcription LAMP whereas chemokine levels were determined by Magnetic Luminex Screening Assay. Overall, PM was associated with increased plasma levels of CXCL-13 and CXCL-16 and low levels of CXCL-4 and CCL-24 in both peripheral and placental blood (0.0002 <= p <= 0.042). Similarly, CCL-24 levels in peripheral and placental blood samples were significantly lower in submicroscopically infected women compared to healthy controls (p = 0.04 and 0.02, respectively). Maternal hemoglobin levels increased with peripheral plasma levels of CXCL-4 (p = 0.005), CXCL-16 (p = 0.03), and CCL-24 (p = 0.002) while birth weight was lower for babies born from women with high levels of peripheral CXCL-13 (p = 0.0006) and low levels of cord CXCL-4 and CCL-24 (p = 0.02 and 0.08, respectively). Together the data suggest that low levels of CXCL-4 and CCL-24 coupled with high plasma levels of CXCL-13 and for a lesser extend CXCL-16 represent signatures of PM in the study population. These findings are relevant for understanding the immunopathogenesis of PM and developing new therapeutic or preventive strategies against severe PM outcomes.