Beyond macrophages: FIPV tropism includes T and B lymphocytes, 2026, Balakumar et al.

[Chandelier]

Beyond macrophages: FIPV tropism includes T and B lymphocytes

Spoiler: Authors

Balakumar, Aadhavan; Wanakumjorn, Patrawin; Kimura, Kazuto; McLarty, Ehren; Farrell, Katherine; Brostoff, Terza; Pires, Jully; Cohen-Davidyan, Tamar; Cassano, Jennifer M.; Murphy, Brian; Reagan, Krystle; Kol, Amir

Highlights​

• FIPV infects monocytes/macrophages and also enters T and B lymphocytes in cats with effusive FIP.
• Single-cell RNA sequencing and confocal imaging reveal FIPV RNA and nucleocapsid protein in T and B lymphocytes.
• Subgenomic FIPV RNA is detected in CD3⁺ T, indicating active viral RNA replication.
• FIPV RNA–positive lymphocytes uniquely activate antiviral and innate immune pathways, supporting true cellular infection.
• Low-level FIPV RNA persists in lymphocytes after antiviral therapy despite clinical resolution.

Abstract​

If untreated, feline infectious peritonitis (FIP) is a fatal disease that is caused by feline infectious peritonitis virus (FIPV), a virulent biotype of feline coronavirus (FCoV) that disseminates broadly and triggers severe systemic inflammation.

While the prevailing model holds that FIPV selectively infects monocytes/macrophages, the full range of susceptible cell types and the mechanisms of immune cell invasion remain poorly defined.

Here, we applied single-cell RNA sequencing, multiplex immunofluorescence, and in situhybridization to mesenteric lymph node aspirates and formalin fixed and paraffin embedded lymph node tissues from cats with naturally occurring effusive FIP.

We identified FIPV RNA and nucleocapsid protein in T and B lymphocytes and myeloid cells, and subgenomic viral RNA in T cells, demonstrating cell entry and viral genomic replication across multiple immune compartments.

Rare FIPV RNA–positive lymphocytes persisted after antiviral treatment cessation and resolution of clinical signs.

These findings revise current models of FIPV pathogenesis and reveal new insights into coronavirus-driven immune dysregulation, viral persistence, and relapse.

Our study highlights the utility of FIP as a naturally occurring animal model for exploring adaptive immune cell infection in coronavirus diseases, providing a translational platform for understanding virus–host interactions that drive chronic or relapsing immunopathology.

Graphical Abstract​

Web | DOI | Veterinary Microbiology

 

[Chandelier]

Cat Disease Challenges What Scientists Thought About Coronaviruses

A UC Davis study shows a deadly cat coronavirus infects multiple immune cells, helping explain persistent inflammation and long COVID–like illness.

www.ucdavis.edu

AI Summary:

Cat Disease Challenges What Scientists Thought About Coronaviruses​

Study Finds Viruses May Hide and Persist in Immune Cells​

Researchers at the University of California, Davis uncovered new details about feline infectious peritonitis, a once-deadly coronavirus disease in cats.
The disease is caused by a feline coronavirus that changes inside some cats and is almost always fatal if untreated.
Lychee, a domestic long-haired cat, participated in a UC Davis clinical trial that cured him of FIP.
Scientists long believed the virus infected only one type of immune cell.
The new study found viral material in several immune cells, including B and T lymphocytes.
Researchers also observed that the virus was actively replicating inside these cells.
Lymph node samples from cats with naturally occurring FIP were used to make these findings.
The study was published in the journal Veterinary Microbiology.
Researchers found that viral traces could remain in immune cells even after treatment and apparent recovery.
Because some immune cells live for years, this persistence may help explain long-term illness or relapse.