Vitamin D, wonder drug

We've discussed vitamin D on the bayblab before, particularly as a cancer fighter and it's possible link to seasonal affective disorder (SAD). Recent research has shown that a single dose of vitamin D can give a long term preventative effect against the mycobacteria that causes tuberculosis.

A related mycobacterium found in the soil, Mycobacterium vaccae has been shown to improve mood by activating the peripheral immune system leading to serotonin release (published in Neuroscience). Do vitamin D's reported mood altering effects work the same way: by activating the immune system?