Immunohistochemical study of monocyte chemoattractant protein-1 in the pancreas of NOD mice following cyclophosphamide administration and during spontaneous diabetes

In type 1 diabetes mellitus (T1DM), the processes which control the recruitment of immune cells into pancreatic islets are poorly defined. Complex interactions involving adhesion molecules, chemokines and chemokine receptors may facilitate this process. The chemokine, monocyte chemoattractant protein-1 (MCP-1), previously shown to be important in leukocyte trafficking in other disease systems, may be a key participant in the early influx of blood-borne immune cells into islets during T1DM. In the non-obese diabetic (NOD) mouse, the expression of MCP-1 protein has not been demonstrated. We employed dual-label immunohistochemistry to examine the intra-islet expression, distribution and cellular source of MCP-1 in the NOD mouse following cyclophosphamide administration. NOD mice were treated with cyclophosphamide at day 72–73 and MCP-1 expression studied at days 0, 4, 7, 11 and 14 after treatment and comparisons were made between age-matched NOD mice treated with diluent and non-diabetes-prone CD-1 mice. Pancreatic expression of MCP-1 was also examined in NOD mice at various stages of spontaneous diabetes. In the cyclophosphamide group at day 0, MCP-1 immunolabelling was present in selective peri-islet macrophages but declined at day 4. It increased slightly at day 7 but was more marked from day 11, irrespective of diabetes development. The pattern of MCP-1 expression in macrophages was different over time in both the cyclophosphamide and control groups. In the cyclophosphamide group, there was a change over time with an increase at day 11. In the control group, there was little evidence of change over time. There was no significant difference in the mean percentage of MCP-1 positive macrophages between the cyclophosphamide-treated diabetic and non-diabetic mice. During spontaneous diabetes in the NOD mouse, only a few peri-islet MCP-1 cells appeared at day 45. These became more numerous from day 65 but were absent at diabetes onset. We speculate that a proportion of early islet-infiltrating macrophages which express MCP-1 may attract additional lymphocytes and macrophages into the early inflamed islets and intensify the process of insulitis.