THE ROLE OF ANTI-HLA CLASS I ANTIBODIES IN GRAFT OUTCOME:
REJECTION VERSUS ACCOMMODATION
S. Ali, Fatmah M. A. Naemi, V. Carter, J. A. Kirby
Institute of Cellular Medicine, Medical School, Newcastle University, Newcastle upon
Tyne, NE2 4HH, UK.
Background: The development of anti-donor HLA class I antibody after organ transplantation has
been associated with acute rejection and is a risk factor for chronic rejection. However, under certain
circumstances transplanted organs acquire a resistance to antibody toxicity by a process called
accommodation. Although different lines of evidence have shown that anti-HLA class I antibody
might activate various signal transduction pathways in graft endothelial cells, the exact mechanism is
not fully understood. This study was designed to assess the potential of anti-HLA class I antibody to
activate endothelial cell signaling mediators leading to a change in immunogenicity.
Methods:
Human
microvascular
endothelial
cells
(HMEC-1)
were
characterized
by
immunofluorescence and flow cytometry. HMEC-1 cells were treated with a saturating concentration
of anti-HLA class I antibody (W6/32, 12μg/ml) and examined to assess the activation of various
protein kinases using a human phosphokinase array. Specific activation of candidate cell signaling
mediators was then confirmed by Western blotting.
Results: Ligation of anti-HLA class I molecules on HMEC-1 cells stimulated activation of several
kinases. However, two of these molecules (CREB and Akt) showed a particularly strong response. The
relevance of these molecules for cell activation was assessed by specific inhibitors. No effect on cell
proliferation was observed after 48 hours stimulation. However, treatment of cells with W6/32
monoclonal antibody resulted in expression of ICAM-1 and VCAM-1 (p<0.05) with a maximum
increase at 48h. Furthermore, restimulation of antibody-treated cells with TNFα (10ng/ml) for 16h
modulated the expression of these adhesion molecules. Future experiments will determine the ability
of renal transplant patient sera to modify the expression of these adhesion molecules.
Conclusion: Exposure of endothelial cells to anti-HLA class I antibodies activates several
transduction pathways and transcription factors which might modulate the function of endothelium
post-transplantation. These findings suggest that anti-HLA antibodies have the capacity to transduce
signals in endothelial cells that may promote the development of chronic rejection.