Abstract:
Decidual macrophages play a vital role during pregnancy, contributing to immune tolerance, tissue priming, remodeling, and parturition. Any alteration in the placental microenvironment that affects the polarization state of these cells can lead to significant adverse effects during pregnancy. Malaria, a highly inflammatory disease, can occur within the placenta and is likely to disrupt the carefully regulated immunological responses associated with pregnancy. Macrophages are the second most abundant immune cells in the placenta, following uterine natural killer (uNK) cells, and are essential for maintaining a healthy pregnancy. This study determined the distribution of M1 and M2 macrophage responses in placentas from infected versus uninfected participants, assessed the expression of transcription and angiogenic factors involved in M1 and M2 pathways, and determined how the pattern in placentas from malaria-infected versus uninfected participants correlated with M1/M2 cytokine production with Th1/Th2. The study enrolled women aged 18 to 45 years (n = 66) who attended antenatal clinics at Webuye County Hospital, Bungoma, Western Kenya. Upon delivery, placentas and dry blood spots (DBS) of placental blood were collected. DBS was used for malaria diagnosis. Following collagenase digestion, placental samples were used as the source of macrophages and other immune cells for downstream characterization. The recovered immune cells were analyzed by flow cytometry for surface markers, including CD68, CD80, CD86, CD163, CD206, and CD209. For gene expression analysis, macrophages were isolated from immune cells using anti-CD14 beads, and the levels of transcription and angiogenic factors were analyzed by quantitative real-time PCR (qRT-PCR), targeting the following genes: STAT1, IRF5, STAT6, cMAF, ANG1, and ANG2. This was achieved by stimulating both T cells and macrophages to express cytokines using PMA-ionomycin and LPS, respectively, to understand the functionality of these cells. Sixty-six pregnant mothers were enrolled in this study. Out of this, 26 (44.07%) were malaria-positive by histology, while 27 were positive by PCR (46.55%). The highest proportion of pregnant mothers was among those aged 20-35 (71.20%). Malaria was associated with younger mothers (P=0.037). Low birth weight was recorded in 11.90% of the newborns. M2 macrophages were significantly expressed in the placentas in all groups (women with and without malaria) (P=0.0001). There were no significant differences in both the M1 and M2-like macrophage markers (CD68, P=0.5586; CD80, P=0.7282; CD86, P=0.9641; CD206, P=0.9122 + and CD163/CD206, P=0.4441), indicating that malaria infection did not have any impact on these responses. Notably, the gene expression levels of the angiogenic factors ANG-1 (P = 0.0396) and the M2 transcription factor STAT-6 (P = 0.0116) were significantly higher in the malaria-negative population. While no significant differences in cytokine expression were observed between the two groups, a trend toward increased TNF-α expression (P = 0.0457) was observed in the malaria-positive group. Interestingly, there was a reduction in the expression of IL-10 and IL-4. This study highlights the crucial role of placental macrophages in malaria infection, revealing an immune signature that has been largely overlooked. It reveals that reduced ANG-1 expression serves as a marker for placental malaria (PM), while lower STAT-6 levels in malaria-infected individuals suggest improved protection against PM and contribute to a healthy pregnancy. The findings presented here may be explored as a potential alternative therapeutic option.
