Here's another interesting area to keep an eye on, namely the apparent importance of IL-15 for bioconversion of 5-hydroxyvitamin D3 (25D3) into bioactive 1,25D3 and the downstream induction of cathelicidins:

• IL-15 links TLR2/1-induced macrophage differentiation to the vitamin D-dependent antimicrobial pathway.<

"In this study, we found that TLR2/1-induced IL-15 was required for induction of CYP27b1, the VDR and the downstream antimicrobial peptide cathelicidin.  Although both IL-15 and IL-4 triggered macrophage differentiation, only IL-15 was sufficient by itself to induce CYP27b1 and subsequent bioconversion of 25-hydroxyvitamin D3 (25D3) into bioactive 1,25D3, leading to VDR activation and induction of cathelicidin"

Here's another study along these lines:

• IL-15 mediates antigen-induced neutrophil migration by triggering IL-18 production<

"Together, these results demonstrate that IL-15 plays an important role in antigen-induced neutrophil migration during inflammationⁱ<i<, triggering a sequential OVA, IL-15, IL-18, MIP-2, MIP-1alpha, TNF-alpha, LTB4 and neutrophil migration signaling cascade"

There are quite a few other studies in pubmed showing the importance of IL-15 in fighting infectionsⁱ<i<.  Here are a couple:

• IL-15-induced CD8+CD122+ T cells increase antibacterial and anti-tumor immune responses: implications for immune function in aged mice.<
• Interleukin-15 increases Paracoccidioides brasiliensis killing by human neutrophils.<

Unfortunately, some drugs seem to inhibit IL-15, and researchers are on the hunt for additional IL-15 inhibitors to treat "inflammatory" diseasesⁱ<i<:

• Cyclosporine differentially regulates interleukin-10, interleukin-15, and tumor necrosis factor a production by rheumatoid synoviocytes.<
• A new orally active anti-rheumatic drug targets IL-15 and IL-17<