In vivo depletion of CD4+CD25+ regulatory T cells in cats

Abstract

To establish a characterized model of regulatory T cell (Treg) depletion in the cat we assessed the kinetics of depletion and rebound in peripheral and central lymphoid compartments after treatment with anti-CD25 antibody as determined by cell surface markers and FOXP3 mRNA expression. An 82% decrease in circulating CD4+CD25+ Tregs was observed by day 11 after treatment. CD4+CD25+ cells were also reduced in the thymus (69%), secondary lymphoid tissues (66%), and gut (67%). Although CD4+CD25+ cells rebound by day 35 post-treatment, FOXP3 levels remain depressed suggesting anti-CD25 antibody treatment has a sustainable diminutive effect on the Treg population. To determine whether CD25+ Treg depletion strategies also deplete activated CD25+ effector cells, cats were immunized with feline immunodeficiency virus (FIV) p24-GST recombinant protein, allowing them to develop a measurable memory response, prior to depletion with anti-CD25 antibody. Anti-FIV p24-GST effector cell activity in peripheral blood after depletion was sustained as determined by antigen-specific T cell proliferation and humoral responses against FIV p24-GST with an ELISA for antigen-specific feline IgG. Furthermore, development of an anti-mouse response in Treg-depleted cats was similar to control levels indicating the retained capacity to respond to a novel antigen. We conclude that despite alterations in CD25+ cell levels during depletion, the feline immune system remains functional. We demonstrate here a model for the study of disease pathogenesis in the context of reduced numbers of immunosuppressive CD4+CD25+ Tregs throughout the feline immune system.

Partial Regulatory T Cell Depletion Prior to Acute Feline Immunodeficiency Virus Infection Does Not Alter Disease Pathogenesis

“…(Figure 9C). This suggests that FoxP3 upregulation was followed by CD25 expression and a transition of cells to the phenotype CD4 + CD25 + known to harbor activated, suppressive Treg cells in the cat [22]. This idea is supported by adoptive transfer studies in the mouse showing that de novo Treg cell generation during acute malaria infection was not due to proliferation of CD25 + FoxP3 + cells or differentiation of CD25 − FoxP3 − cells but rather was the result of proliferation of CD25 − FoxP3 + cells that simultaneously began expressing CD25 [62].…”

CD4+CD25+T Regulatory Cells Inhibit CD8+IFN-γ Production During Acute and Chronic FIV Infection Utilizing a Membrane TGF-β-Dependent Mechanism

“…LN biopsies were performed as previously described. 21,44 Briefly, cats were anesthetized with intravenous ketamine and valium and anesthesia was maintained with isofluorane gas. Popliteal lymph nodes were excised through a small incision in the caudal aspect of the stifle and the incision was sutured with monofilament sutures.…”

Feline immunodeficiency virus latency

“…FIV has been shown to preferentially infect CD4 + CD25+ activated/regulatory T-cells (Tregs) [80], which correlates with both surface CXCR4 expression and binding of cellular transcription factors to the FIV promoter [81]. Feline Tregs have since been characterized using FoxP3 [82,83], so these studies are merely suggestive of infection in that subset. Importantly, the FIV receptor CD134 (OX40) is constitutively expressed on Tregs [84], lending support to this hypothesis.…”

“…Finally, the ability of the immune system to adequately respond and kill reactivated cells is critical to proposed strategies to purge viral reservoirs. Selective depletion of CD4 + CD25+ cells has been shown to result in improved antiviral responses in cats chronically infected with FIV [83,86], which could potentially be part of a strategy to boost the immune system during or after ALT. There is much still to be learned about these and other interactions between the immune system and latent FIV.…”