| | Isoform | Structure | Molecular weight | Function | Expression | Reference |
| IL-37
All forms | Exons 1 to 6 | 17~25 kDa | Suppress immune responses
Potential antitumor effect
Not completely clear | Expressed in human, not detected in mice
Yes in the following:
Tissues: plasma cells in epithelial crypts and germinal centres of tonsils, lamina propria of colon, plasma cells of tonsil germinal centres and tonsil epithelial cells, skin sweat glands, skin sebaceous glands, colon epithelium, normal breast cells, placental syncytial trophoblast, skin epidermal cells, blood monocytes, keratinocytes in stratum granulosum of skin
Organs: testis, thymus, uterus, muscle, brain, thalamus, lung, spleen, prostate, placenta; low levels in heart, adrenal glands, stomach, liver, salivary glands, pancreas, kidney
Cell lines: PBMC, A431, THP-1, U937, IMTLH, KG-1, HL60, HPBMC, HPT-4, RAJI, SK-LU-1, CCL-247, NHDC
Carcinomas: stroma of colon carcinomas, breast carcinomas, some colon carcinoma cells, melanomas, lung carcinomas, ductal mammary carcinoma, hepatocellular carcinoma
No in the following:
Prostate carcinoma cells, blood lymphocytes | [2–4, 9, 11–13, 21] |
| IL-37a
Isoform 5 | Exon 3 (prodomain) and exons 4 to 6 | 21.55 kDa | Anti-inflammatory effect
Not completely clear | Yes in the following:
Tissues and organs: lymph nodes, thymus, bone marrow, placenta, colon, lung, testis, placenta, colon, brain
Cell lines: THP-1, U937, HL60, IMTLH, HPT-4
Carcinomas: colon carcinoma
No in the following:
Spleen, tonsil, foetal liver, liver, heart, skeletal muscle, kidney, pancreas, prostate, ovary, small intestine, leukocytes, T lymphocytes, B lymphocytes | [2, 4, 9, 11, 12] |
| IL-37b
Isoform 1 | Exons 1 and 2 (prodomain) and exons 4 to 6 | 24.13 kDa | Suppresses immune responses and inflammation
Potential antitumor effect | Yes in the following:
PBMC, lymph nodes, placenta, colon, lung, testis, kidney
No in the following:
brain, heart | [2–4, 11, 12] |
| IL-37c
Isoform 4 | Exons 1 and 2 (prodomain) followed by exons 5 and 6 | 19.61 kDa | May not have biological functions Downregulates IL-37b and IL-37d | Yes in the following:
lymph nodes, placenta, colon, lung, testis, heart
No in the following:
brain, kidney | [2, 4] |
| IL-37d
Isoform 2 | Exon 1 and exons 4 to 6 | 21.95 kDa | Unknown | Yes in the following:
testis, bone marrow
No in the following:
lymph nodes, placenta, colon, lung,brain, kidney, heart | [2, 4] |
| IL-37e
Isoform 3 | Exons 1, 5, and 6 | 17.46 kDa | May not have biological functions
Downregulates IL-37b | Yes in the following:
testis, bone marrow
No in the following:
lymph nodes, placenta, colon, lung, brain, kidney, heart | [2, 4] |
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