How does Vitamin C work in boosting immunity?

I don't know about C...but E and Garlic are better for your immune system.

The trials proved that vitamin C is more effective for children. Reports from the field confirm the observations in the trials and suggest that children are less prone to vitamin C side effects. Colds and flu are a serious problem for children. Every time a cold infects a child, its growing mind and body must divert energy from its usual business of growth and development. If the cold is followed by an opportunistic infection, such as bronchitis or ear infection, more energy must be diverted. Colds are the number one trigger for asthma. Pre-school children in daycare are nearly constantly fighting infections (5-10 per year). Chronic disease in childhood is believed to sometimes have permanent developmental consequences which can contribute to decreased life expectancy. In 2002 a meta-study into all the published research on effectiveness of ascorbic acid in the treatment of infectious disease and toxins was conducted, by Thomas Levy, Medical Director of the Colorado Integrative Medical Centre in Denver. He claimed that evidence exists for its therapeutic role in a wide range of viral infections and for the treatment of snake bites. If vitamin C can help to fight viral infections, it it evident such vitamin helps in enhancing the immune system as well.

All I can say is it seems works for me. I take an extract of Camu Camu berry (most concentrated known source of natural vitamin c) I learned about at http://www.bartenblends.com and I haven't really been sick since I started taking it a year ago, and I get sick several times a year. Though the berry is also known to contain many powerful antioxdidants, so maybe that is also a factor.