Looks like Anti Histamines could affect the innate immune system in fighting infections.

Effects of antihistamines on innate immune responses to severe bacterial infection in mice.

http://www.ncbi.nlm.nih.gov/pubmed/21346365

"The safety profile of antihistamines may need to be revisited."

http://www.ncbi.nlm.nih.gov/pubmed/21807405

Medication with antihistamines impairs allergen-specific immunotherapy in mice.

http://www.ncbi.nlm.nih.gov/pubmed/18081882

Long-term exposure to glucocorticoid medications, such as asthma and anti-inflammatory medication, has been shown to create deficits in memory and attention both during and, to a lesser extent, after treatment,^[10][11] a condition known as "steroid dementia."^[12]

http://en.wikipedia.org/wiki/Glucocorticoid