The image of the month is a fluorescent antibody-based display of the glomerulus; the main filtrating unit within the kidney generated in the HPA group in Uppsala. The image is a result of a multiplex immunohistochemistry staining, where the podocyte protein podocin (gene: NPHS2) and five other proteins specific to different main structures within the kidney were stained and visualized through fluorescently tagged antibodies.

Multiplex immunohistochemistry (mIHC/IF) allows for simultaneous spatial visualization of different proteins in a single tissue section. In this way, the overlap between a protein of interest and multiple cells/structures within an organ can be visualized in order to localize the protein in the tissue at the single cell level. In the latest version of the HPA, mIHC antibody panels were used to visualize proteins within kidney and testis.

Podocin (NPHS2) is a membrane associated protein found in specialized epithelial cells, called podocytes, that cover the capillaries of the filtrating glomeruli inside of the kidney. The podocytes form thin gaps between each other in the form of zipper-like alternating foot processes, called slit diaphragms, that works as sieves to prevent larger molecules, such as proteins, from leaving the blood circulation, while smaller molecules, such as salts and sugars, are excreted into the urine. Podocin is believed to be a necessary structural component of the slit diaphragm, supported by the development of childhood steroid-resistant nephrotic syndrome with focal segmental glomerulosclerosis as a consequence of mutations in the NPHS2 gene. The multiplex immunofluorescent staining of podocin in kidney shows clear staining overlap between the antibody towards podocin (green) and the staining of the outer podocyte layer of glomeruli (yellow).More in depth information about the technique can be found here!