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Cystine and cysteine modulate immune system

Cystine is an amino acid composed from two cysteine molecules connected by a sulfuric bond. The amino acid cysteine, as such, is one of the direct precursors of glutathione, a key antioxidant and immune-supporting molecule, and its supply is considered to be a rate-limiting factor in glutathione synthesis. The small peptide glutathione is synthetized from cysteine and glutamate.

Several ways of providing those two amino acids have been explored to keep glutathione availability high during situations when immune system should be up-regulated (for example in common cold). Since orally-provided glutamate is mostly metabolized in the gut; theanine (an amino acid-like molecule derived from green tea) has been used as a means to increase circulating glutamate levels. In initial rodent experiments, a combination of cystine and theanine increased glutathione synthesis and enhanced resistance to influenza infection (www.ncbi.nlm.nih.gov/pubmed/19940390 ). In elderly humans, co-administration of cystine and theanine before influenza vaccination improved the immune response to the vaccine in those subjects who were characterized by low serum total protein and hemoglobin and who were therefore especially vulnerable o infections (www.ncbi.nlm.nih.gov/pubmed/19149835). Comparably, in younger people who were subjected to long-distance run, the combination of cysteine and theanine efficiently attenuated the reduction in lymphocyte count and overall drop in immune reactivity invariably induced by intense endurance exercise (www.ncbi.nlm.nih.gov/pubmed/20525371). Some of those positive results could be perhaps explained as a secondary consequence of glutathione stimulation, as hypothesized recently by Dr. Kurihara and colleagues (www.ncbi.nlm.nih.gov/pubmed/24312747 ).

While more detailed analysis of the action mechanism is necessary, the amino acid cysteine, in a combination with theanine, may lead to improved vaccination efficacy in older people with reduced immunological functions. Also, it may serve as a dietary supplement for those who wish to maintain their physical condition throughout the year or to athletes in endurance disciplines. Attention to appropriate dosing of cysteine is warranted.