Development of a specific system for targeting protein to metallophilic macrophages.

The cysteine-rich domain (CR) of the mannose receptor binds sulfated glycoprotein CR ligand (CRL) expressed by subpopulations of myeloid cells in secondary lymphoid organs (CRL(+) cells). In naïve mice, these CRL(+) cells, metallophilic macrophages (M) in spleen and subcapsular sinus M in lymph nodes, are located strategically for antigen capture and are adjacent to B cell follicles, but their role in the immune response is unknown. We have exploited the lectin activity of CR to develop a highly specific system for targeting protein to CRL(+) M. We demonstrate that the sulfated carbohydrates recognized by CR are exposed to the extracellular milieu and mediate highly specific targeting of CR-containing proteins. This model will allow the dissection of the role of metallophilic M in an immune response in vivo.