SEMA4D and rheumatoid arthritis: Thus, it is theorized that the identification of a soluble form of Sema4D detected in the GCF of patients with PD [32], as well as serum Sema4D found in rheumatoid arthritis and postmenopausal osteoporosis [34], results from cleaving of membrane-bound Sema4D expressed on the cell surface [35].