Background: Human immunodeficiency virus (HIV) remains a significant life-threatening agent and burden on public health. Lesser studied and understood aspects of HIV include HIV-associated inflammatory arthritis and the role NK cells and cytokines like GM-CSF have on its development. By utilizing humanized mice with human cytokine knockins that better support a human immune system than other models, we studied HIV-associated arthritis to better understand its development and progression.

Objectives: Determine the etiology of HIV-associated inflammatory arthritis including cellular involvement and cytokines which can be used as therapeutic targets.

Methods: MISTRG-IL15 mice[1] (human M -CSF/GM-CSF, I L-3, S IRPα, T PO, R AG2 -/-, I L2rg-/-, and IL-15 knocked into the respective endogenous mouse loci) were reconstituted with CD34+ hematopoietic stem cells obtained from human fetal cord blood. After checking for engraftment after 6-8 weeks, we infected reconstituted mice with HIV. Synovial tissues were obtained from the knee joints of the hind limbs at different time points and processed into single cell suspensions. Intercellular staining was performed on cells incubated with PMA/Ionomycin for 4 hours and then permeabilized and fixed for flow cytometry. NK cells were defined as CD3-CD56+. Histochemistry was also performed on hind paws that were fixed in 4% paraformaldehyde. Samples were then sectioned and stained with H&E for histologic analysis. Studies also involved depletion of NK cells and macrophages, Antiretroviral therapy (ART), and viral strains with unique tropisms.

Results: The majority of humanized MISTRG-IL15 mice developed inflammatory arthritis after HIV infection. Significant increases in total inflammatory cells and NK cells were seen in the synovial tissue throughout the course of infection. GM-CSF producing NK cells also increased throughout the course of HIV infection. Late in the course of infection, IFNγ- and granzyme B-producing NK cells increased, along with a pro-inflammatory environment in the synovial tissue. Histologic analysis showed increased cellular infiltrate in the synovium by at 8 weeks of infection with erosive changes. ART eliminated cellular infiltration while cessation of therapy resulted in return of cellular infiltration in synovial tissue. Use of a chemokine receptor-tropic HIV virus that does not infect macrophages (X4-tropic) or depletion of macrophages showed reduced pro-inflammatory cytokine production by NK cells, strongly suggesting HIV-infected macrophages induced the NK cell responses. Depletion of NK cells resulted in blockade of development of inflammatory arthritis.

Conclusion: We have found a unique role of GM-CSF produced by NK cells contributing to the development of HIV-associated inflammatory arthritis in our unique mouse model. In addition to providing a model to study arthritis induced by other human pathogens, findings from such studies will provide mechanistic understanding of inflammatory arthritis.

REFERENCES: [1] Sungur CM, Wang Q, Ozantürk AN, Gao H, Schmitz AJ, Cella M, Yokoyama WM, Shan L. Human NK cells confer protection against HIV-1 infection in humanized mice. J Clin Invest. 2022 Dec 15;132(24):e162694. doi: 10.1172/JCI162694. PMID: 36282589; PMCID: PMC9753998.

Acknowledgements: Dr. Wayne Yokoyama and Dr. Liang Shan from Washington University.

Disclosure of Interests: None declared.