Assembly of the cell surface IL-10 receptor complex is the first

Assembly of the cell surface IL-10 receptor complex is the first step in initiating IL-10 signaling pathways that regulate intestinal inflammation viral persistence and even tumor surveillance. in their receptor sequences (Bazan 1990; Ho et al. 1993; Walter 2004). IL-10 is a unique class 2 cytokine because it potently inhibits the production of pro-inflammatory cytokines such as IFNγ tumor necrosis factor α (TNFα) IL-1β and IL-6 in a several cell types and prevents dendritic cell (DC) maturation in part by inhibiting the expression of IL-12 (Chang et al. 2004; Moore et al. 2001). IL-10 also inhibits the expression of MHC and co-stimulatory molecules important for cell-mediated immunity (Moore et al. 2001). However IL-10 also exhibits immunostimulatory activities that include the ability to stimulate IFNγ production in CD8+ T cells activated with anti-CD3/anti-CD28 or other cytokine cocktails (Mumm et al. 2011; Santin et al. 2000). IL-10 is also a potent growth and differentiation factor for B-cells mast cells and thymocytes (Moore et al. 2001; Rousset et al. 1992; BI 2536 Thompson-Snipes et al. 1991). IL-10 cellular responses require the specific recognition and assembly of a heterodimeric cell surface complex comprised of IL-10R1 and IL-10R2 chains (Fig. 1) (Kotenko et al. 1997). IL-10R1 BI 2536 is an ~80 0 kDa protein with an extracellular ligand binding domain (ECD) of 227 residues a transmembrane helix of 21 residues and an intracellular domain (ICD) of 322 amino acids (Liu et al. 1994). The ECD of IL-10R2 is about the same length as IL-10R1 consisting of BI 2536 201 residues (Lutfalla et al. 1993). However the ICD of IL-10R2 consists of only 83 residues. The IL-10R1 ECD forms specific high affinity interactions (surface plasmon resonance (SPR) analyses are in good agreement. Although IL-10R2 is essential for the biological activity of cIL-10 (Kotenko et al. 1997) cIL-10 cell binding affinity does not change whether the IL-10R2 chain is expressed on cells or not (Ding et al. 2001). Subsequent SPR studies estimated the cIL-10/IL10R2 binding affinity to Abarelix Acetate be approximately 3mM (Logsdon et al. 2002). Additional binding studies measured an ~13-fold increase in the affinity of soluble IL-10R2 (KD = 234μM) for the cIL-10/IL-10R2 binary complex relative to cIL-10 alone (Yoon et al. 2005). Even with the ~13-fold affinity increase IL-10R2 interaction is approximately four orders of magnitude weaker than the cIL-10/IL-10R1 site 1 interaction. As a result of the disparate IL-10R1 and IL-10R2 affinities each receptor chain has a distinct function in activating IL-10 cellular responses. Specifically IL-10R1 functions as the IL-10 binding chain which controls cell specificity and cellular targeting of IL-10 to immune cells that selectively express the IL-10R1 chain (Nagalakshmi et al. 2004; Wolk et al. 2002). The second function of the IL-10R1 chain is to regulate receptor occupancy time which is controlled by the kinetics of the IL-10/IL-10R1 interaction. In contrast to IL-10R1 IL-10R2 functions as a sensor chain which efficiently “senses” IL-10 bound to IL-10R1 (.e.g. the IL-10/IL-10R1 complex). Thus the role of the IL-10R2 chain is to BI 2536 activate signaling based on the kinetics of the IL-10/IL-10R1 interaction. Because of its singular function IL-10R2 can be used in similar signaling strategies of the other IL-10R2 binding cytokines IL-22 IL-26 IL-28a/b and IL-29 (Donnelly et al. 2004; Jones et al. 2008; Yoon et al. 2010). This allows specific signaling responses from 6 cytokines using 5 receptors. Thus the promiscuous binding IL-10R2 with its singular function reduces the number of unique receptor chains required for IL-10 family cytokine signaling. Not surprisingly changes in site 1 (IL-10/IL-10R1) or site 2 (IL-10/IL-10R2) interfaces result in different biological results (Ding et al. 2001; Raftery et al. 2004; Yoon et al. 2012; Yoon et al. 2006). Disruptions in IL-10 site 1 increases the effective concentration of the ligand required to induce one half of measured maximal biological reactions (EC50). Despite improved EC50 ideals site 1 mutants can still induce biological responses equivalent to cIL-10 at high protein concentrations (Yoon et al. 2012). In contrast mutations in IL-10 site 2 cannot induce the same response levels observed for cIL-10 despite the addition of extremely high protein concentrations (Yoon et al. 2006). However consistent with BI 2536 the low affinity of the IL10R2 chain most mutations in IL-10 site 2 have little impact on IL-10 signaling whereas most mutations made in the high affinity site 1 cause a measurable.