No difference was found in salivary levels of selected markers of the immune system in volunteers exposed or sham-exposed to 900 MHz for 4-hour periods (Radon, 2001).

One report suggested that a 30 minute exposure to radiation from a cell phone could change immune markers of latex allergy in patients with eczema who were allergic to this substance (Kimata, 2005).

References:

Authors
Augner C, Hacker GW, Oberfeld G, Florian M, Hitzl W, Hutter J, Pauser G.
Title
Effects of Exposure to GSM Mobile Phone Base Station Signals on Salivary Cortisol, Alpha-Amylase, and Immunoglobulin A.
Journal
Biomed Environ Sci. (2010). 23(3):199-207.

Authors
Radon K, Parera D, Rose D-M, Jung D, et al.
Title
No effects of pulsed radio frequency electromagnetic fields on melatonin, cortisol, and selected markers of the immune system in man.
Journal
Bioelectromagnetics 2001;22:280-287.
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Author
Kimata H.
Title
Microwave radiation from cellular phones increases allergen-specific IgE production.
Journal
Allergy 2005;60:838-9
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Authors
Aly AA, Cheema MI, Tambawala M, Laterza R, Zhou E, Rathnabharathi K, Barnes FS.
Title
Effects of 900-MHz Radio Frequencies on the Chemotaxis of Human Neutrophils in Vitro.
Journal
IEEE Transactions on Biomedical Engineering. 2008;55(2 part1): 795-797.