No abstract

Peripheral blood can be a valuable source of adult stem cells, if one can identify reliable equine-specific markers, provide methods to increase the number of circulating progenitor cells and optimise cell culture conditions for growth and viability. Our findings are important for further studies towards technological advances in basic and clinical equine regenerative medicine.

Purpose To determine whether activated CD11b+ CD15+ granulocytes increase in the blood of patients with uveal melanoma. Methods Peripheral blood mononuclear cells (PBMCs) were isolated by density gradient centrifugation from the blood of patients with primary choroidal/ciliochoroidal uveal melanomas (six women, four men; age range, 46–91 years) and healthy control donors (14 women, 10 men; age range, 50 – 81 years). The expression of CD15 and CD68 on CD11b+ myeloid cells within PBMCs and primary uveal melanomas was evaluated by flow cytometry. CD3ζ chain expression by CD3ε+ T cells in PBMCs and within primary uveal melanomas was measured as an indirect indication of T-cell function. Results The percentage of CD11b+ cells in PBMCs of patients with uveal melanoma increased 1.8-fold in comparison to healthy donors and comprised three subsets: CD68 negative CD15+ granulocytes, which increased 4.1-fold; CD68− CD15− cells, which increased threefold; and CD68+ CD15low cells, which were unchanged. A significant (2.7-fold) reduction in CD3ζ chain expression on CD3ε+ T cells, a marker of T-cell dysfunction, was observed in PBMCs of patients with uveal melanoma in comparison with healthy control subjects and correlated significantly with the percentage of CD11b+ cells in PBMCs. CD3ζ chain expression on T cells within primary tumors was equivalent to CD3ζ expression in PBMCs of the same patient in four of five patients analyzed. Conclusions Activated CD11b+ CD15+ granulocytes expand in the blood of patients with uveal melanoma and may contribute to immune evasion by ocular tumors by inhibiting T-cell function via decreasing CD3ζ chain expression.

Ocular immune privilege (IP) limits immune surveillance of intraocular tumors as certain immunogenic tumor cell lines (P815, E.G7-OVA) that are rejected when transplanted in the skin grow progressively when placed in the anterior chamber (a.c.) of the eye. As splenectomy (SPLNX) is known to terminate ocular IP, we characterized immune mechanisms responsible for rejection of intraocular tumors in SPLNX mice as a first step toward identifying how to restore tumoricidal activity within the eye. CD8+ T cells, IFNγ, and FasL, but not perforin, or TNFα were required for elimination of intraocular E.G7-OVA tumors that culminated in destruction of the eye (ocular phthisis). IFNγ and FasL did not target tumor cells directly as the majority of SPLNX IFNγR1−/− mice and Fas defective lpr mice failed to eliminate intraocular E.G7-OVA tumors that expressed Fas and IFNγR1. Bone marrow chimeras revealed that IFNγR1 and Fas expression on immune cells was most critical for rejection and SPLNX increased the frequency of activated macrophages (Mϕ) within intraocular tumors in an IFNγ-and-Fas/FasL-dependent manner suggesting an immune cell target of IFNγ and Fas. As depletion of Mϕs limited CD8 T cell-mediated rejection of intraocular tumors in SPLNX mice, our data support a model in which IFNγ-and-Fas/FasL-dependent activation of intratumoral Mϕs by CD8+ T cells promotes severe intraocular inflammation that indirectly eliminates intraocular tumors by inducing phthisis, and suggests that immunosuppressive mechanisms which maintain ocular IP interfere with the interaction between CD8+ T cells and Mϕs to limit immunosurveillance of intraocular tumors.

Immunosuppressive molecules within the aqueous humor (AqH) are thought to preserve ocular immune privilege by inhibiting pro-inflammatory nitric oxide (NO) production by macrophages (Mϕs). Consistent with previous observations, we observed that although Mϕs stimulated in the presence of AqH expressed NO-synthase-2 (NOS2) protein, nitrite concentrations in culture supernatants, an indirect measure NO production, did not increase. Interestingly, NOS2 enzymatic activity, as measured by the conversion of L-arginine (L-Arg) into L-citrulline, was augmented in lysates of Mϕs stimulated in the presence of AqH. These data suggested that intracellular L-arg may have been limited by AqH. However, we observed increased mRNA expression of the L-arg transporter, CAT2B, and increased L-arg uptake in Mϕs stimulated in the presence of AqH. Arginases were expressed by stimulated Mϕs but competition for L-arg with NOS2 was excluded. Expression of GTP cyclohydrolase which produces tetrahydrobiopterin (H4B), an essential cofactor for NOS2 homodimerization, increased after Mϕ stimulation in the presence or absence of AqH and NOS2 homodimers formed. Taken together these data provided no evidence for inhibited NOS2 enzymatic activity by AqH suggesting that a factor within AqH may have interfered with the measurement of nitrite. Indeed, we observed that nitrite standards were not measurable in the presence of AqH and this effect was due to ascorbate in AqH. Controlling for interference by ascorbate revealed that AqH augmented NO production in Mϕs via ascorbate which limited degradation of H4B. Therefore, AqH may augment NO production in macrophages by stabilizing H4B and increasing intracellular L-Arg.