Since inflammatory mechanisms have been postulated to link obesity to osteoarthritis, the current
study evaluated the ratio of immune cells to multipotent stromal cells within the infrapatellar fat
pad (IPFP) and subcutaneous adipose tissue (SQ) of the knee; each depot has potential as a source
of regenerative cells. The immunophenotypes of stromal vascular fraction (SVF) and adipose-derived
stem cells (ASCs) of the IPFP and SQ were determined in tissues from osteoarthritic subjects (n=7)
undergoing total knee replacement. Based on a subset of surface antigens, the immunophenotype of
ASCs from SQ of OA subjects was not significantly different from that of relatively healthy and leaner
subjects undergoing elective liposuction surgery. Flow-cytometry comparison of SVF cell populations
in the IPFP of OA subjects resembled those within the subject’s own matched SQ, with the exception
of the endothelial marker CD31+, which was significantly greater in cells from SQ. In the OA subjects,
lower numbers of capillary-like structures and higher numbers of stromal and alkaline phosphatase
colony-forming units in the IPFP vs SQ were consistent with this finding; however, ASCs from both
depots in OA subjects exhibited comparable adipogenic and osteogenic differentiation potential.
Thus, the IPFP contains an ASC and immune cell population similar to that of donor-matched SQ,
making it an alternative ASC source for tissue regeneration. Further studies will be needed to
determine whether IPFP immune cell infiltrates play an aetiological role in osteoarthritis equivalent
to that shown in diabetes associated with obesity.