Detection of the Tim-3 ligand, galectin-9, inside the allograft during a rejection episode

Tim-3 is a Th1 lymphocytes membrane protein with inhibitory function. Its ligand, galectin-9, was recently identified and it is expressed in some lymphocyte subpopulation. In addition, endothelial cells and fibroblasts can also express galectin-9 according to the local cytokine milieu. Both molecules can act as important regulatory tools in the immune system.

Evaluate the expression of these immunoregulatory molecules inside kidney allografts during acute rejection episodes.

By using a quantitative polymerase chain reaction assay, we measured the levels of messenger RNA (mRNA) for galectin-9 and Tim-3 in 21 samples obtained at allograft nephrectomy. Five samples received the histological diagnosis of acute non-vascular rejection (ANVR), twelve of acute vascular rejection (AVR), and five of loss of non-immune cause (LNIC; as control). As cytolytic response markers we measured mRNA levels of granzyme B, interferon-gamma and perforin. The statistic analysis was performed using one way analysis of variance (ANOVA) and Pearson correlation.

The mean levels of Tim-3 mRNA expression were 13.99+/-6.99 for LNIC, 48.13+/-54.47 for RACNV and 238.63+/-333.14 for RAV (p=0.004). For galectin-9, the mean values were 0.57+/-0.49 for LNIC, 0.66+/-0.36 for RACNV and 2.34+/-1.62 for RAV (p=0.006). Furthermore, there was a positive correlation between both molecules (r=0.526, p=0.016). Also, granzyme B, perforin and interferon-gamma mRNA expression were different among the three groups.

Messenger RNA level expressions of all the studied molecules were higher inside allografts with more severe rejection. Moreover, there was a positive correlation between galectin-9 and Tim-3 mRNA levels. The simultaneous expression of galectin-9 and Tim-3 may indicate an immunoregulatory function, during the ongoing cytotoxic response.