Abstract
Purpose: :
Macrophages (Mϕs) can be characterized into pro-inflammatory M1 and anti-inflammatory M2 phenotypes. While Mϕs are known to reside within the mouse cornea, nothing is known regarding the distribution of M1 and M2 phenotypes in normal and wounded corneas.
Methods: :
A 2mm diameter central epithelial region was mechanically debrided from the corneas of anesthetized female C57Bl/6 WT mice (n=20). After injury (24, 48, 72h and 7days), corneas were immunostained with antibodies raised against mouse Mϕ markers (F4/80, CD115, CD163, CD206, CX3CR1, together with known M1 markers CD80, CD86 and M2 marker CD301). Immunostained corneas were imaged as wholemounts and Mϕ numbers were counted at the limbus (L), paralimbus (PL), parawound (PW), wound (W) and wound center (WC). Uninjured corneas were used for comparison.
Results: :
In all corneas, while CD80+ cells (M1) were negative for most Mϕ markers, they were positive for CX3CR1. This contrasts with CD301+ cells (M2) which were distinctly negative for CX3CR1 and CD86 yet positive for all other Mϕ markers (F4/80, CD115, CD163, and CD206). Interestingly, throughout the corneal stroma, a third Mϕ phenotype (F4/80+) was identified which was negative for both CD301 and CD80. In uninjured cornea, CD301+ Mϕs were found at the L and PL. 24h after wounding, CD301+ Mϕ numbers declined by 50% at the L (P<0.01) but remained unchanged at the PW, W and WC. By 48h and 72h post-injury, CD301+ Mϕ numbers returned to baseline at the L but their numbers increased at the PL, PW, W and WC. Seven days after wounding, CD301+ Mϕ numbers showed a second decline to 67% of baseline at the L(P<0.01) while their numbers in the remaining corneal regions returned to baseline values. At all post-injury times, CD80+ cell numbers remained unchanged and these cells were only detected within the L.
Conclusions: :
Both CD80+ and CD301+ Mϕs exist in normal and wounded corneas. CD80+ Mϕs appear to be restricted to the limbus while CD301+ Mϕs show a greater capacity for infiltrating the wounded cornea. The identification of additional F4/80+CD301-CD80- cells suggests M1 and M2 polarization is not a characteristic feature of all corneal macrophages.
Keywords: cornea: basic science • inflammation • microscopy: light/fluorescence/immunohistochemistry