CD40 ligand increases complement C3 secretion by proximal tubular epithelial cells.

Area of Science:

• Nephrology
• Immunology
• Cell Biology

Background:

• Interstitial leukocyte infiltration is a hallmark of tubulointerstitial damage (TID).
• Proximal tubular epithelial cells (PTEC) interact with infiltrating lymphocytes via soluble factors and cell contact.
• CD40 on PTEC can be engaged by CD40L on T cells, and PTEC secrete C3, potentially promoting TID.

Purpose of the Study:

• To investigate the effect of CD40 ligation on C3 secretion by PTEC.
• To determine the synergistic effects of CD40 ligation with soluble factors like IL-1beta and IFN-gamma.

Main Methods:

• Primary human PTEC and HK-2 cells were cultured and stimulated with IL-1beta, IFN-gamma, and/or CD40L-expressing cells.
• C3 gene expression was analyzed using RT-PCR and Northern blot.
• Secreted C3 was quantified via ELISA and functional hemolytic assays.
• NF-kappaB pathway involvement was assessed using a specific inhibitor (CAPE).

Main Results:

• IL-1beta and IFN-gamma alone increased PTEC C3 expression and secretion (2-3 fold).
• CD40L stimulation upregulated C3 secretion by four-fold in HK-2 cells.
• The combination of IFN-gamma and CD40L resulted in a potent 30-fold increase in C3 secretion.
• NF-kappaB inhibition reduced CD40L-induced C3 secretion by 70%.

Conclusions:

• CD40 ligation enhances C3 secretion by PTEC.
• This cell contact mechanism synergizes with T cell-derived IFN-gamma.
• CD40L-induced C3 secretion may amplify TID associated with lymphocyte infiltration.