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Background and objectives: Neuropilin-1 (NP-1), a functional vascular endothelial growth factor (VEGF) receptor, is important in the priming of resting T cells and contributes to the development of peripheral tolerance. Semaphorins, a family of axon guidance molecules, has been found to be involved in regulating the immune system.The aim of this study was to explore the involvement of NP-1 and semaphorins in lupus glomerulonephritis (LGN).Methods: Twelve kidney biopsies from LGN patients and five normal biopsies were examined in this study. In addition, eight biopsies from patients with primary nephropathy and proteinuria were included serving as a disease control group. Biopsies were stained with anti-VEGF, NP-1, and semaphorins. The Image Pro-Plus software was used to measure the intensity and extent of staining. The correlation with clinico-pathological parameters was evaluated.Results: VEGF expression was slightly higher in LGN. NP-1 and semaphorins were stained with significantly higher intensity in LGN when compared with both the normal and the disease control groups. NP-1 deposits were found only in damaged glomerulus areas and positively correlated with clinico-pathological parameters of renal disease (a statistical trend). However, the semaphorins were found in inverse correlations.Discussion: Being present in normal and slightly increased in diseased glomeruli, VEGF is considered protective during inflammation. Increased NP-1 expression in LGN may intensify the possible protective effect of VEGF, thereby preventing endothelial damage. However, one should consider the possibility that increased NP-1 expression is harmful and could play a role in the damage of LGN. NP-1 is suggested to be a reliable marker differentiating focal versus diffuse LGN. Semaphorin 3A can serve as a histological marker for tubular damage. The altered ability of kidneys to secrete semaphorins during advanced renal damage may in part explain its inverse correlation with renal function. Further work is needed in order to better understand the role of NP-1 and semaphorins in LGN. [ABSTRACT FROM AUTHOR]