Persistent infection contributes to heterologous protective immunity against fatal ehrlichiosis

Area of Science:

• Immunology
• Microbiology
• Infectious Diseases

Background:

• Human monocytotropic ehrlichiosis (HME) is a severe tick-borne illness caused by Ehrlichia chaffeensis.
• Mouse models using Ehrlichia muris (persistent) and Ixodes ovatus Ehrlichia (IOE, lethal or sublethal) are used to study HME.
• Persistent E. muris infection confers protection against lethal IOE challenge, unlike sublethal IOE infection.

Purpose of the Study:

• To investigate the role of persistent infection in maintaining protective memory immune responses against ehrlichiosis.
• To determine if eradicating persistent ehrlichial infection impacts heterologous protection.

Main Methods:

• Mice with persistent E. muris infection were treated with doxycycline or left untreated.
• Both groups were subsequently challenged with a lethal dose of IOE.
• Immune responses, including T-cell populations and cytokine production, were analyzed in spleens.

Main Results:

• Untreated, persistently infected mice exhibited higher numbers of antigen-specific gamma interferon-producing splenic memory T cells and expanded CD4(+) CD25(+) T regulatory cells compared to doxycycline-treated mice.
• Persistent infection correlated with increased transforming growth factor beta1 production in the spleen.
• Doxycycline treatment significantly reduced the protective effect of E. muris priming against lethal IOE challenge.

Conclusions:

• Persistent ehrlichial infection is crucial for sustaining memory T-cell responses that confer heterologous protection.
• Eradication of persistent ehrlichial infections may compromise long-term immunity against related pathogens.