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Inhibiting cytokines of the interleukin‐12 family: recent advances and novel challenges

Interleukin‐12 (IL‐12) and the more recently discovered IL‐23 and IL‐27 constitute a unique family of structurally related, heterodimeric cytokines that regulate cell‐mediated immune responses and T helper 1 (Th1)‐type inflammatory reactions. Not surprisingly, the potentiality of treating conditions such as multiple sclerosis (MS) and rheumatoid arthritis (RA) through pharmacological interference with IL‐12 pathways has received widespread attention. In this review we have examined over 50 substances with reported IL‐12 inhibitory effects. We demonstrate that a majority of these belong to a limited number of major functional classes, each of which targets discrete events in the IL‐12 biological pathway. Thus, most IL‐12 inhibitory substances appear to work either through inhibition of transcription factor NF‐κB activation, up‐regulation of intracellular cAMP, blockage of posttranslational processing or interference with signal transduction pathways. In addition, cyclophilin‐binding drugs, and generic inhibitors of nuclear histone deacetylases, and of ion channels, pumps and antiporters are emerging as potential leads to novel targets for interference with IL‐12 production. Many inhibitors of NF‐κB and of IL‐12 signal transduction have been proven effective in limiting or preventing disease in experimental autoimmune encephalomyelitis (EAE) models of MS. The sharing of the p40 subunit, the IL‐12Rβ1 and components of the signal transduction pathways between IL‐12 and IL‐23 raises the question as to whether the beneficial effects of various drugs previously ascribed to inhibition of IL‐12 may, in fact, have been due to concurrent blockage of both cytokines, or of IL‐23, rather than IL‐12. Moreover, the homodimeric β2‐form of IL‐12, though originally considered to display only antagonistic effects, is now emerging as a pronounced agonist in a variety of inflammatory processes. Reassessment of IL‐12 inhibitory compounds is therefore needed to scrutinize their effects on IL‐12 αβ, β2 and IL‐23 formation. This is likely to open exciting perspectives to the identification of drugs that target these cytokines either indiscriminately or selectively. The functional diversity of presently available inhibitors should facilitate an unprecedented flexibility in designing future trials for the treatment of IL‐12‐ and IL‐23‐mediated disorders.

IFNG polymorphisms are associated with gender differences in susceptibility to multiple sclerosis

Interferon-gamma (IFNγ) treatment is deleterious in multiple sclerosis (MS). MS occurs twice as frequently in women as in men. IFNγ expression varies by gender. We studied a population-based sample of US MS patients and ethnicity-matched controls and independent Northern Irish and Belgian hospital-based patients and controls for association with MS, stratified by gender, of an intron 1 microsatellite [I1(761)*CAn], a single nucleotide polymorphism 3′ of IFNG [3′(325)*G → A] and three flanking microsatellite markers spanning a 118 kb region around IFNG. Men carriers of the 3′(325)*A allele have increased susceptibility to MS compared to noncarriers in the USA (P=0.044; OR: 2.58, 95% CI: 0.97–8.08) and Northern Ireland (P=0.019; OR: 2.37, 95% CI: 1.10–5.13). There is a nonsignificant trend in the same direction in Belgian men (P=0.299; OR: 1.50, 95% CI: 0.71–3.26). Men carriers of I1(761)*CA13, which is in strong linkage disequilibrium with the 3′(325)*A, have increased susceptibility (P=0.050; OR: 2.22, 95% CI: 0.98–5.40), while men carriers of I1(761)*CA12 have decreased susceptibility (P=0.022; OR: 0.46, 95% CI: 0.23–0.90) to MS in the USA. Similar associations were reported in Sardinia between the I1(761)*CA12 allele and reduced risk of MS in men. Flanking markers were not associated with MS susceptibility. Polymorphisms of IFNG may contribute to differences in susceptibility to MS between men and women.

Polymorphisms in the interleukin-4 and IL-4 receptor genes and multiple sclerosis: a study in Spanish-Basque, Northern Irish and Belgian populations.

Cytokine gene polymorphisms are known to influence susceptibility and disease course of many autoimmune diseases. Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system white matter characterized by inflammation, demyelination and axonal damage. We analysed both the well‐known intronic variable number of tandem repeat (VNTR) and +33 C/T single‐nucleotide polymorphisms (SNP) in the IL‐4 gene, as well as the functional Q551R SNP in the IL4‐R gene in a cohort of three distinct populations comprising sporadic cases and controls from the northern Spanish Basque Country and Northern Ireland, as well as family trios from Belgium. The IL‐4 +33 TT genotype was decreased in primary progressive (PP) versus relapsing‐remitting (RR) patients in the Northern Irish population (OR = 0.14; 95% CI = 0.018–1.09). Two‐marker haplotype distribution of the VNTR and +33 C/T SNP in PP patients differed from that seen in RR patients in Northern Ireland (P = 0.03). The R allele of the Q551R SNP was significantly under‐transmitted in the Belgian trio families (P = 0.003), although this effect was not seen in the Northern Irish and Basque data sets. We did not identify IL‐4–IL4‐R gene–gene interaction in determining susceptibility or clinical parameters of MS. Disease or genetic heterogeneity or both may be responsible for the observed lack of reproduction in different populations. Our data reinforce recent findings for a role of IL4‐R in susceptibility to MS.

The metallopeptide antibiotic bacitracin inhibits interleukin‐12 αβ and β2 secretion

The metalloantibiotic bacitracin is a known inhibitor of protein disulfide isomerase (PDI). The disulfide‐linked interleukin‐12 (IL‐12) αβ‐heterodimer and β2‐homodimer forms are crucial mediators of cell‐mediated immune responses and inflammatory reactions. Bacitracin was found to potently block secretion of both the αβ‐ and β2‐dimer forms of IL‐12, while it did not affect secretion of the β‐monomer. This inhibition coincided with a reduction in the intracellular amount of PDI found in complex with the β‐chain during intracellular transit. Bacitracin did not affect mRNA levels of the α‐ and β‐chain. Similar to bacitracin, N‐acetylcysteine blocked αβ‐ and β2‐secretion as well as PDI‐β‐chain complex formation. Thus, blocking PDI or shifting the endoplasmic reticulum towards a more reduced status disrupts the oxidative folding pathway or assembly of IL‐12 dimer forms. The assembly stage of cytokines in the endoplasmic reticulum may represent a novel target for pharmacological intervention.