 Losing collagen is a normal aging process. But for some people, such as those who develop osteoarthritis or rheumatoid arthritis, collagen loss can lead to intense pain and limited mobility. There are ways to manage symptoms, medicines for pain relief, and injections that help lubricate. But outside of total joint replacement, these treatments tend to fall short of a long-term solution. This unmet medical need has driven many scientists to look to the body itself. In a recent study published in Scientific Reports, researchers explained how blood cells whose main job is to patrol for intruders can moonlight as collagen producers, offering a possible new way to combat arthritis. These are peripheral blood mononuclear cells. Known for the large, round nucleus at their center, cells of this type are the main drivers of our immune response, activating and transforming to meet our body's needs. Surprisingly, that includes making type 2 collagen, found exclusively in cartilage. This extraordinary ability was artificially induced when researchers supplemented mononuclear cells with a substance known as macrophage colony-stimulating factor. This substance is an important part of the immune system that stimulates the formation of white blood cells, namely M2 macrophages. M2 macrophages are known combatants of inflammation throughout the body. They're the anti-inflammatory counterpart to M1 macrophages, which tend to promote inflammation. The type 2 collagen-stimulating effect was found to be dose-dependent with macrophage colony-stimulating factor. To determine whether these modified macrophages could replicate this feat in a living body, the research team transplanted them into rats induced to develop arthritis. The limbs of these rats were then compared to those of arthritic rats injected with saline. Measurement showed that in rats with arthritis, the modified macrophages could dramatically reduce swelling in the hind limbs and the paws. Whether similar effects might be observed in humans remain to be seen, but several clinical trials are already underway. If replicated, the findings could be transformative. Encouraging the body's own cells to produce collagen could inspire entirely new ways of treating arthritis and, at least in part, slowing the consequences of aging.