Intravitreal invading cells contribute to vitreal cytokine milieu in proliferative vitreoretinopathy

Aim-To examine the contribution of infiltrating cells in the local producti on of cytokines within the vitreous of patients with proliferative vitreore tinopathy (PVR). Methods-The presence of mRNA coding for IL-6, IL-8, IL-1 beta, IL-1 alpha, TNF alpha, IFN gamma, IL-12, and HPRT was investigated in 25 vitreous sampl es from patients with PVR, 11 vitreous samples from patients with retinal d etachment (RD) not complicated by PVR, and 10 vitreous samples from patient s with macular hole (MH). A quantitative reverse transcriptase polymerase c hain reaction (RT-PCR) using an internal competitor was used to investigate these samples. From these samples, 15 PVR, 8 RD, and 8 MH were analysed fo r the protein levels of the same cytokines using enzyme linked immunosorben t assay (ELISA). Spearman correlation was used to test any association betw een mRNA and cytokine protein levels, as an indicator of the contribution t hese cells make to the intravitreal cytokine milieu. Results-A strong correlation was found between mRNA and their respective cy tokine levels (protein products) for IL-6, IL-8, IL-1 beta, IL-1 alpha, TNF alpha, IFN gamma (Spearman r = 0.83, 0.73, 0.67, 0.91, 0.73, and 0.73 resp ectively), but not for IL-12. The median levels of IL-6, IL-8, IL-1 beta, a nd IFN gamma mRNA and their respective cytokines were significantly higher (p <0.05) in patients with PVR than in those with macular hole. There was n o statistically significant difference in the median levels of IL-1<alpha> mRNA between PVR and MH but the cytokine IL-1 alpha was detected at a signi ficantly higher level in PVR compared with MH patients. Between PVR and RD patients, there was no statistically significant difference in mRNA levels for all the investigated cytokines (p >0.05) except for IL-6 where there wa s a statistical significance (p=0.038). In contrast, the median levels of I L-6, IL-8, and IL-1 beta cytokines were significantly higher (p <0.05) in p atients with PVR than in those with RD, whereas for IL-1<alpha> and IFN gam ma no significant statistical difference was detected between PVR and RD pa tients (p >0.05). When results of RD and MH patients were compared, a stati stical difference was only detected in mRNA levels of INF gamma (p = 0.008) . However, no difference was detected for INF gamma (protein product) or fo r any of the other cytokines between RD and MH patients. Conclusion-Levels of both protein and mRNA encoding IL-6, IL-8, IL-1 beta, and IFN gamma is significantly increased in vitreous samples from patients with PVR. The strong correlation between ELISA detectable cytokines (protei n products) and their respective mRNA levels suggest that intravitreal, inv asive cells are the major source of these cytokines, with the exception of IL-12. Cells invading the vitreous do not appear to locally produce IL-12 m RNA. This would appear to implicate cells peripheral to the vitreal mass as the major source of this cytokine.