The cytokine migration inhibitory factor (MIF) has recently emerged as an important effector molecule of innate immune responses and sepsis. Two functional MIF promoter polymorphisms, a 5–8 CATT tetranucleotide repeat at -794 (CATT5–8) and a -173*G/C single nucleotide polymorphism, have been associated with susceptibility to and/or severity of rheumatoid arthritis, atopy and ulcerative colitis. Our objective was to study the impact of MIF gene polymorphisms on susceptibility to Neisseria meningitidis sepsis and to analyze the functional and biological effects of MIF polymorphisms in vitro.
A case–control study of 1,106 children and adults with meningococcal sepsis and 626 control subjects and a family-based study (106 families with one afflicted child) to analyze transmission of MIF alleles using the transmission disequilibrium test. The -794 CATT5–8 microsatellite and -173*G/C single nucleotide polymorphism were detected by PCR. MIF promoter alleles cloned into a luciferase reporter construct were tested in resting and stimulated THP-1 human monocytic cells. DNA binding activity was assessed by EMSA.
Compared with control subjects, the frequency of the CATT5–5 genotype was markedly reduced in meningococcal sepsis patients (5.3% versus 8.8%; OR = 0.6, 95% CI = 0.4–0.9, P = 0.01 for CATT5–5 versus all other CATTx-x). The frequencies of the -173*G/G, -173*G/C or -173*C/C genotypes was comparable in meningococcal sepsis patients and control subjects (P = 0.75). The transmission disequilibrium test in families with one afflicted child revealed that the CATT5 allele was preferentially not transmitted (P = 0.002) to meninogoccal sepsis offspring, while the opposite situation occurred for the CATT6 allele (P = 0.024). In vitro studies showed lower activity of CATT5 promoter compared with all other CATT promoters in resting and N. meningitidis-stimulated THP-1 cells. Consistently, DNA binding activity to the CATT region of the MIF promoter increased with an increasing number of the CATT repeats.
The frequency of the -794 CATT5–5 genotype was reduced in children with meningococcal sepsis and was less frequently transmitted from parents to affected offspring, suggesting that it may confer protection against severe sepsis due to N. meningitidis. Reduced transcription factor DNA-binding activity to CATT5 and weaker CATT5 promoter transcriptional activity provided a functional relevance of the CATT5 polymorphism. MIF polymorphisms might help to identify patients who may benefit from anti-MIF treatment strategies.