# LL-37 selectively targets Plasmodium-infected erythrocytes and exhibits antimalarial activity

## TL;DR

LL-37, a human antimicrobial peptide, selectively kills malaria-infected red blood cells and shows antimalarial potential in mice.

## Contribution

LL-37/CRAMP selectively targets infected cells via membrane disruption, revealing a novel host defense mechanism against malaria.

## Key findings

- LL-37 selectively kills Plasmodium-infected erythrocytes by targeting membrane alterations like PS externalization and cholesterol depletion.
- LL-37/CRAMP administration in mice reduces parasitemia, improves survival, and modulates pro-inflammatory cytokines.
- CRAMP-deficient mice show increased susceptibility to malaria, confirming its role in host defense.

## Abstract

Malaria control is challenged by the emergence of resistance to virtually all antimalarial drugs, from the frontline artemisinin to other classes, highlighting the critical need for new therapies. This study demonstrates that the human antimicrobial peptide LL-37 exhibits antiplasmodial activity against both drug-sensitive and drug-resistant parasites in vitro. LL-37 selectively targets infected red blood cells through membrane disruption mediated by phosphatidylserine externalization and cholesterol depletion. Elevated plasma LL-37/CRAMP levels were observed in malaria patients and infected mice, and exogenous LL-37/CRAMP administration reduced parasitemia, improved survival, and modulated pro-inflammatory cytokine levels in a mouse model. CRAMP-deficient mice showed higher susceptibility to infection, underscoring its role in host defense. Our findings reveal a naturally occurring host defense mechanism centered on LL-37/CRAMP, which acts through direct targeting of the infected erythrocyte membrane. However, therapeutic administration after infection establishment showed limited efficacy, likely due to rapid peptide degradation in vivo, and the effective concentrations required for direct killing in vitro are substantially higher than endogenous systemic levels. The reduction in systemic cytokines observed in treated mice is likely primarily attributable to decreased parasite burden rather than direct immunomodulation. Further studies are needed to evaluate stabilized analogs, optimized delivery strategies, and combination approaches before therapeutic applications can be considered.

Malaria remains a life-threatening disease, with rising drug resistance undermining current treatments. Host defense peptides like LL-37 offer promising alternatives, but their anti-malarial mechanisms and safety profiles are not fully understood. Here, we show that LL-37 selectively kills malaria parasite-infected red blood cells (iRBCs) by targeting two key membrane alterations caused by Plasmodium infection: phosphatidylserine (PS) externalization and cholesterol depletion. These changes make iRBCs vulnerable to LL-37-mediated lysis, while uninfected RBCs remain protected. We validate this mechanism by reversing the alterations—replenishing cholesterol or blocking PS with DOTAP—both of which reduce LL-37’s anti-parasitic activity. Importantly, LL-37 and its mouse homolog CRAMP exhibit minimal toxicity to uninfected cells in vitro and in vivo, with no detectable hemolysis in treated mice. In a malaria mouse model, LL-37/CRAMP suppress parasitemia and reduce disease severity. Our findings reveal a novel, host-friendly mechanism for LL-37’s anti-malarial action, highlighting its potential as a targeted therapy that bypasses drug-resistance pathways, offering new hope for combating drug-resistant malaria.