IL1RAcP: A universal and indispensable co-receptor in autoimmunity and tumor microenvironments

• Gene Information: The IL1RAP gene (Interleukin-1 receptor accessory protein) is a protein-coding gene located on chromosome 3q28. Unlike specific primary receptors, IL-1RAcP acts as a universal, shared co-receptor essential for the signaling of multiple IL-1 family cytokines, predominantly pairing with IL-1R1, IL-33R (ST2), and IL-36R.
• Protein Expression: IL-1RAcP is broadly and constitutively expressed across various tissues, including epithelial cells, endothelial cells, and nearly all innate and adaptive immune cells (such as T cells, macrophages, and neutrophils). Notably, it is also frequently overexpressed on certain cancer stem cells.
• Signaling Pathway: Upstream activation begins when a primary cytokine (e.g., IL-1, IL-33, or IL-36) binds to its specific primary receptor. This event recruits IL-1RAcP to form a functional heterodimeric complex.
• Therapeutic Inhibition: This "master switch" blockade provides a powerful, multi-pathway inhibition strategy for severe autoimmune diseases and tumor microenvironment modulation.

IL1RAcP

• A chimeric CDS that encodes human IL1RAcP signal peptide and extracellular domain, mouse IL1RAcP transmembrane and cytoplasmic domain is inserted after the 5’UTR of mouse Il1racp gene in B-hIL1RACP mice.
• The chimeric IL1RAcP protein expression will be driven by endogenous mouse Il1racp promoter, while mouse Il1racp gene transcription and translation will be disrupted.

• Mouse Il1racp mRNA was only detectable in wild-type mice.
• Human IL1RAcP mRNA was exclusively detectable in homozygous B-hIL1RAcP mice but not in wild-type mice.

Strain specific analysis of IL1RAcP gene expression in wild-type C57BL/6 mice and homozygous humanized B-hIL1RACP mice by RT-PCR. Liver was collected from wild-type C57BL/6 mice (+/+) and homozygous B-hIL1RACPmice (H/H), then cDNA libraries were synthesized by reverse transcription, followed by PCR with mouse or human IL1RAcP primers. Mouse Il1racp mRNA was detectable only in wild-type C57BL/6 mice. Human IL1RAcP mRNA was detectable only in homozygous B-hIL1RACP mice, but not in wild-type C57BL/6 mice.

• Human IL1RACP was exclusively detectable in homozygous B-hIL1RACP mice, but not in wild-type C57BL/6 mice.

Strain specific IL1RACP expression analysis in wild-type C57BL/6 mice and homozygous humanized B-hIL1RACP mice by flow cytometry. Splenocytes were collected from wild-type C57BL/6 mice and homozygous B-hIL1RACP mice. Protein expression was analyzed with anti-human IL1RACP antibody (R&D, FAB676P) by flow cytometry. Human IL1RACP was exclusively detectable in homozygous B-hIL1RACP mice, but not in wild-type C57BL/6 mice.

• Murine IL1/IL33/IL36 protein effectively activated splenocytes in wild-type mice and triggered the secretion of related cytokines.
• Murine IL1B and murine IL33 proteins could effectively activate splenocytes in B-hIL1RACP mice and trigger the secretion of related cytokines, while murine IL36 protein could not effectively activate B-hIL1RACP mice splenocytes.

Splenocytes were collected from wild-type mice and homozygous B-hIL1RAcP mice and stimulated with IL1/IL33/IL36 protein. The expression of cytokines in splenocytes culture medium was detected after 48 hours. The results showed that murine IL1/IL33/IL36 protein effectively activated splenocytes in wild-type mice and triggered the secretion of related cytokines. Murine IL1B and murine IL33 proteins could effectively activate splenocytes in B-hIL1RACP mice and trigger the secretion of related cytokines, while murine IL36 protein could not effectively activate B-hIL1RACP mice splenocytes.

Experimental schedule for IMQ-induced psoriasis model in B-hIL1RAcP mice. Mice at 7 week-old of age received a daily topical of commercially available IMQ cream on the shaved back for 6 consecutive days to induce IMQ-induced psoriasis model. Control mice were treated similarly with Vaseline cream. Severity of skin inflammation was daily scored and back skin was collected at the endpoint. IMQ: imiquimod.

• After treatment of CAN10-analog, the phenotypical presentation level and erythema and scaling score of the back were much lower than the control in homozygous B-hIL1RAcP mice.

IMQ-induced skin inflammation in B-hIL1RAcP mice phenotypically resembles psoriasis. Mice (female, 7 week-old, n=5) were scored daily for up to 7 days for body weight and clinical signs of skin inflammation following treatment with imiquimod (IMQ) cream. Mice in each group were treated with CAN10-analog (10 mpk, in-house). (A) Experimental schedule for induction of psoriasis-like skin lesions (B) Phenotypical presentation of mouse back skin at day 6. (C) Body weight during treatment. (D-E) Erythema and scaling score of the back was scored daily. Additionally, the cumulative score (erythema plus scaling) is depicted. Values are expressed as mean ± SEM. Significance was determined by two-way ANOVA test. ***P < 0.001.  

• CAN10-analog had therapeutic effects on psoriasis-like skin lesions in B-hIL1RAcP mice, confirming that B-hIL1RAcP mice provide a powerful model for in vivo evaluation of anti-human IL1RAcP antibodies.

Dose dependent effects of antibodies on historical score in IMQ induced psoriasis-like skin lesions in B-hIL1RAcP mice. Back skin was collected at the endpoint and stained with Hematoxylin and eosin (H&E). (A) H&E staining of the back skin. (B) Histological changes were scored. Results indicated that the CAN10-analog (10 mpk, in-house) significantly improved psoriasis-like skin parameters, including hyperkeratosis, crusting, and acanthosis, confirming that B-hIL1RAcP mice provide a powerful model for in vivo evaluation. Values are expressed as mean ± SEM. ***P < 0.001.

Experimental schedule of MSU-induced peritonitis model in B-hIL1RAcP mice. Male B-hIL1RAcP mice received intraperitoneal (i.p.) administration of Vehicle, CAN10-analog (10 mg/kg), or ALM27134-analog (10 mg/kg) on Day 0 and Day 3. One hour after the initial dosing on Day 0, mice were stimulated with an i.p. injection of MSU to induce the peritonitis model. Samples were collected at the endpoint for efficacy evaluation. MSU: monosodium urate.

• After treatment of CAN10-analog and ALM27134-analog, the number of neutrophils was significantly inhibited and almost returned to the level of the control group in MSU-induced peritonitis model.

Effects of Anti-IL1RAcP antibody on immune cell infiltration in peritoneal lavage fluid in a MSU-induced peritonitis model using B-hIL1RAcP mice. (A) Quantification of mCD45⁺ cells in peritoneal lavage fluid across groups. (B) Total neutrophil counts in peritoneal lavage fluid. (C) Percentage of neutrophils within the mCD45⁺ population, demonstrating that the number of neutrophils was significantly inhibited by CAN10-analog (10 mpk, in house) and ALM27134-analog (10 mpk, in house) and almost returned to the level of the control group. Values are expressed as mean ± SEM. Significance was determined by two-way ANOVA test.  *P < 0.05, **P < 0.01, ****P < 0.0001. Groups G1, G3, and G4 showed significant differences compared to G2.