The potential role of non-classical monocytes in preventing malarial parasitemic recurrence in a mouse model

Background: Frequent recurrence is responsible for persistent Plasmodium infection after the acute stage. Our previous study demonstrated that phagocytic cells are essential for controlling Plasmodium chabaudi chabaudi AS ( P. chabaudi ) recurrence. Nevertheless, the specific type of phagocytic cells involved in controlling P. chabaudi recurrence, as well as their underlying molecular mechanisms of action, remain elusive. Methods: Single-cell RNA sequencing (scRNA-seq) was employed to analyze splenic phagocytic cells during both the acute and recurrent phases of P. chabaudi infection. The frequencies of red pulp macrophages (RPMs), classical monocytes (CMs), and non-classical monocytes (NCMs) were detected by flow cytometry. Low-dose clodronate liposomes (CLs) and CCR2 ^-/- mice were used to investigate the protective role and origin of NCMs. Results: Using scRNA-seq, we found that NCMs declined during the acute stage of P. chabaudi blood-stage infection, and then expanded rapidly in the recurrence stage. The changing trend of NCMs was confirmed by flow cytometry. To explore the potential role of NCMs in controlling parasitemic recurrence, NCMs were selectively depleted by a low-dose of CLs during the recurrence stage, which significantly elevated the P. chabaudi parasitemia. Additionally, no significant difference in the proportion of splenic NCMs or CMs within the monocyte population was observed between the infected CCR2 ^-/- mice and their control littermates, suggesting that the transition from circulating CMs to NCMs may not occur in this model. Conclusions: In summary, our results indicate that NCMs potentially play a protective role in preventing malarial parasitemic recurrence, offering valuable insights into immune-based interventions against Plasmodium infection and potentially contributing to the prevention of malaria transmission.