# Host biological sex directs immune control of the Plasmodium parasite liver stage in mice

## TL;DR

The study shows that biological sex influences how the liver immune system responds to malaria parasites, with males having weaker defenses due to androgens.

## Contribution

The study reveals that androgens and biological sex directly affect immune responses and parasite survival during Plasmodium liver stage infection in mice.

## Key findings

- Intact male mice had reduced immune cell counts and weaker responses to Plasmodium infection compared to females and ORX males.
- Androgens increased parasite survival by reducing the elimination of infected hepatocytes.
- Baseline differences in immune cell composition between sexes persisted and worsened during infection.

## Abstract

Plasmodium parasites, the causative agents of malaria, undergo a complex liver stage shaped by the spatial heterogeneity of the liver. As one of the most sexually dimorphic organs, the liver undergoes sex-specific immune responses. However, the roles of biological sex and androgens in regulating hepatic host–parasite interactions during Plasmodium infection remain poorly understood.

Male and female BALB/cJ mice, including orchiectomized (ORX) and androgen-treated males, were infected with Plasmodium yoelii sporozoites. Hepatic parasite burden, immune cell composition, and gene expression were assessed using immunofluorescence microscopy, RT-PCR, and spatial transcriptomics. Comparisons across sex and androgen status were performed in infected and mock-infected conditions.

Androgens increased parasite survival by reducing elimination of parasite-infected hepatocytes. Females and ORX males exhibited enhanced immune activity during P. yoelii infection, resulting in fewer infected hepatocytes by 44 hours post-infection. At homeostasis, intact males had lower baseline densities of Kupffer cells, monocytes, and dendritic cells, a disparity that persisted and increased during infection. Although infection induced similar fold increases in Kupffer cell numbers across groups, intact males had reduced absolute numbers of Kupffer cells, diminished antigen presentation, and blunted Type I interferon responses compared to female and ORX male mice.

These findings indicate that biological sex- and androgen-mediated differences in baseline hepatic innate immune cell composition critically shape immune responses and parasite survival during Plasmodium liver stage infection. Together, our findings highlight the role of biological sex in shaping immune responses during Plasmodium parasite infection in the liver and underscore the importance of considering sex as a biological variable in malaria research.