IL-4 potentiates IL-1beta- and TNF-alpha-stimulated IL-8 and MCP-1 protein production in human retinal pigment epithelial cells.
OBJECTIVE
Human retinal pigment epithelial (HRPE) cells are involved in ocular inflammation by secretion of chemokines such as IL-8 and MCP-1. It has been shown in this and other laboratories that interleukin-1 beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) are potent inducers of HRPE IL-8 and MCP-1 secretion. The induced IL-8 and MCP-1 expression is often modulated by other proinflammatory factors in a synergistic manner. Modulation of IL-8 and MCP-1 production by interleukin-4 (IL-4), a important mediator in Th2-mediated immunity, and granulocyte/macrophage-colony-stimulating factor (GM-CSF), one of the cytokines secreted by HRPE has been reported in non-ocular cells. The aim of the present investigation was to study effects of these two cytokines alone or in combination with IL-1beta or TNF-alpha on HRPE IL-8 and MCP-1 generation.


METHODS
The primary culture of HRPE cells was stimulated with various doses of IL-4, GM-CSF, IL-1beta and TNF-alpha alone or in combination for 8 or 24 hr. The supernatants were subjected to enzyme-linked immunosorbent assay (ELISA) for IL-8 and MCP-1. The mRNAs were isolated from the corresponding cells for Northern blot analysis.


RESULTS
IL-1beta and TNF-alpha induced dose-dependent increases in HRPE IL-8 and MCP-1 secretion with maximal stimulation observed at 2-5 ng/ml. IL-4 alone (100 ng/ml) resulted in a slight increase of MCP-1 and IL-8 secretion. When IL-4 was co-administrated with IL-1beta or TNF-alpha, two to three-fold increases in IL-8 and MCP-1 were observed over the maximal levels induced by IL-1beta or TNF-alpha alone. Northern blot analyses revealed that IL-4 did not alter the steady-state MCP-1 mRNA stimulated by IL-1beta and TNF-alpha, or alter the IL-8 mRNA stimulated by TNF-alpha, although the IL-1beta-induced IL-8 mRNA was slightly enhanced by higher concentrations of IL-4 (100 ng/ml).


CONCLUSIONS
The synergistic action by IL-4 occurs predominately at the post-transcriptional level. In contrast to IL-4, GM-CSF alone or in combination with IL-1beta or TNF-alpha did not generate additional secretion of HRPE IL-8 and MCP-1. HRPE IL-8 and MCP-1 gene expression and protein production are stimulated by IL-1beta or TNF-alpha through pathways differentially modulated by IL-4 and GM-CSF.
Bian
Z M
ZM
Department of Ophthalmology, University of Michigan, Ann Arbor 48105, USA.
Elner
S G
SG
Strieter
R M
RM
Kunkel
S L
SL
Lukacs
N W
NW
Elner
V M
VM
D002478:Cells, Cultured; D018932:Chemokine CCL2 / Q000096:biosynthesis* / Q000235:genetics; D004338:Drug Combinations; D004357:Drug Synergism; D015870:Gene Expression / Q000187:drug effects; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology*; D015847:Interleukin-4 / Q000494:pharmacology*; D016209:Interleukin-8 / Q000096:biosynthesis* / Q000235:genetics; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D018932:Chemokine CCL2; D004338:Drug Combinations; D007375:Interleukin-1; D016209:Interleukin-8; D014409:Tumor Necrosis Factor-alpha; D015847:Interleukin-4; D016178:Granulocyte-Macrophage Colony-Stimulating Factor