Anti-KLRG1 Monoclonal antibody, clone 3G2 [APC]

Brucella melitensis is a well-adapted zoonotic pathogen considered a scourge of mankind since recorded history. In some cases, initial infection leads to chronic and reactivating brucellosis, incurring significant morbidity and economic loss. The mechanism by which B. melitensis subverts adaptive immunological memory is poorly understood. Previous work has shown that Brucella-specific CD8(+) T cells express gamma interferon (IFN-gamma) and can transition to long-lived memory cells but are not polyfunctional. In this study, chronic infection of mice with B. melitensis led to CD8(+)T cell exhaustion, manifested by programmed cell death 1 (PD-1) and lymphocyte activation gene 3 (LAG-3) expression and a lack of IFN-gamma production. The B. melitensis-specific CD8(+) T cells that produced IFN-gamma expressed less IFN-gamma per cell than did CD8(+) cells from uninfected mice. Both memory precursor (CD8(+) LFA1(HI) CD127(HI) KLRG1(LO)) and long-lived memory (CD8(+) CD27(HI) CD127(HI) KLRG1(LO)) cells were identified during chronic infection. Interestingly, after adoptive transfer, mice receiving cells from chronically infected animals were able to contain infection more rapidly than recipients of cells from acutely infected or uninfected donors, although the proportions of exhausted CD8(+) T cells increased after adoptive transfer in both challenged and unchallenged recipients. CD8(+) T cells of challenged recipients initially retained the stunted IFN-gamma production found prior to transfer, and cells from acutely infected mice were never seen to transition to either memory subset at all time points tested, up to 30 days post-primary infection, suggesting a delay in the generation of memory. Here we have identified defects in Brucella-responsive CD8(+) T cells that allow chronic persistence of infection.

The inhibitory receptor killer cell lectin-like receptor G1 (KLRG1) and the integrin alpha(E) (CD103) are expressed by CD8(+) T cells and both are specific for E-cadherin. However, KLRG1 ligation by E-cadherin inhibits effector T-cell function, whereas binding of CD103 to E-cadherin enhances cell-cell interaction and promotes target cell lysis. Here, we demonstrate that KLRG1 and CD103 expression in CD8(+) T cells from untreated and virus-infected mice aremutually exclusive. Inverse correlation of KLRG1 and CD103 expression was also found in human CD8(+) T cells-infiltrating hepatocellular carcinomas. As TGF-beta is known to induce CD103 expression in CD8(+) T cells, we examined whether this cytokine also regulates KLRG1 expression. Indeed, our data further reveal that TGF-beta signaling in mouse as well as in human CD8(+) T cells downregulates KLRG1 expression. This finding provides a rationale for the reciprocal expression of KLRG1 and CD103 in different CD8(+) T-cell subsets. In addition, it points to the limitation of KLRG1 as a marker for terminally differentiated CD8(+) T cells if lymphocytes from tissues expressing high levels of TGF-beta are analyzed.