Acute Malaria Induces PD1+CTLA4+ Effector T Cells with Cell-Extrinsic Suppressor Function.

Area of Science:

• Immunology
• Infectious Diseases
• Cell Biology

Background:

• Acute Plasmodium falciparum malaria requires precise immune regulation to control parasite levels without causing excessive inflammation.
• Coinhibitory receptors like CTLA4 and PD1 are crucial for modulating T cell responses, but their specific roles in malaria are not well understood.

Purpose of the Study:

• To investigate the function of coinhibitory receptors, specifically CTLA4 and PD1, on CD4+ T cells during acute Plasmodium falciparum malaria.
• To determine if these receptors influence T cell cytokine production and regulatory capabilities in malaria patients.

Main Methods:

• Blood samples were collected from patients with acute P. falciparum malaria and healthy controls.
• Flow cytometry was used to analyze the expression of CTLA4 and PD1 on CD4+ T cells.
• In vitro stimulation with infected red blood cells and blocking antibodies (anti-PD1/PDL1, anti-CTLA4) were employed to assess T cell function and cytokine production (IFNγ, IL10).
• Isolated PD1+CTLA4+CD4+ T cells were tested for their suppressive effects on T cell proliferation.

Main Results:

• CD4+ T cells from malaria patients showed higher expression of CTLA4 and PD1 compared to healthy controls.
• A distinct population of PD1+CTLA4+CD4+ T cells was identified, co-producing IFNγ and IL10 upon stimulation with P. falciparum-infected cells.
• Blocking PD1/PDL1 and CTLA4 pathways enhanced antigen-specific cytokine production.
• Isolated PD1+CTLA4+CD4+ T cells exhibited P. falciparum-specific inhibitory effects on the proliferation of other CD4+ T cells.

Conclusions:

• Acute P. falciparum malaria induces a specific subset of CD4+ T cells (PD1+CTLA4+) that produce both pro-inflammatory (IFNγ) and anti-inflammatory (IL10) cytokines.
• These cells act as regulatory effector T cells, suppressing other CD4+ T cell responses in a malaria-specific manner.
• This transient induction of regulatory effector T cells may be a key mechanism for controlling T cell responses and preventing severe inflammation in malaria and potentially other acute infections.