Our Immune System: The Sixth Sense?

I came across an article implying another link between our immune system, behavior, and psychology, and could not resist digging a little further and sharing what I read.
Although it is often understood, accepted, and sometimes overlooked that someone suffering from either chronic illness, an acute life-changing medical event, or a terminal disease would experience feelings of depression or even, at times, to end their own life - what if, instead, the immune-boosting medications they were taking or the immunological processes at work in their system was supplying the fuel for their depression?
According to McElroy, 12-30 percent of patients of various diseases with an inflammatory component, also suffer from depressive disorders (News Bureau, 7/27/04). Glassman and Miller, similarly, found that "45% of malignant melanoma patients treated with high-dose alpha interferon developed major depression" (Biological Psychiatry, August, 2007). The statistics abound with depression and suicide suspiciously following administration of two immune-boosters - alpha interferon and interleukin-2 (New Scientist, 16 June 2001).
Dantzer and Kelley believe that the cytokines, boosted by drugs, such as those listed above, activate the enzyme indoleamine-2,3-dioxygenase, which catabolizes tryptophan, thereby preventing it from being turned into serotonin - a known brain regulatory chemical and focus of much of the anti-depressant industry today (News Bureau, 7/24/04). They also invoked fever and sickness-related behavior in mice whose brains were directly injected with cytokines and then found that if they blocked pathways from brain to body, they could inhibit these same sickness behaviors (News Bureau, 7/27/04).
Maes found that people suffering from depression had higher than expected immune system markers: natural-killers cells, monocytes, and macrophages, as opposed to an expected supressed immune system (New Scientist, 16 June 2001). There was even evidence from Germany of a possible viral link to depression, though results were unable to be replicated (New Scientist, 16 June 2001).
The vote is still out it seems - Glassman and Miller site inconsistencies and obviously a complex relationship between cytokines and depression, with much left to be identified and understood (Biological Psychiatry, August 2007).
What if depression were somehow linked to viral infection? What if we could prevent depression associated with illness or major medical procedures with the simple administration of SSRIs? Is the immune system really our sixth sense, telling our bodies to display symptoms of illness and depression? The questions seem neverending.

References:

"Scientists Build on Case Connecting Inflammatory Disease and Depression." McElroy, Molly; News Bureau, 7/27/2004, University of Illinois at Urbana-Champaign.
"A Mind Under Seige." Brown, Phyllida; New Scientist, 16 June 2001.
"Where there is Depression, there is Inflammation, Sometimes!" Glassman, Alexander H., and Miller, Gregory E.; Biological Psychiatry, Volume 62, Issue 4, 15 August 2007, Pages 280-281.