Bloody...

...good.

While its primary job is to carry oxygen to and carbon dioxide away from cells, the fact that in doing so it touches all of them has resulted in some fantastic exaptations (evolutionary adaptations in which something that evolved for one purpose is used for another).

These functions include: carrying hormones and other proteins from the site of origin to the site(s) of effect; coagulation; and, most significantly, immunity.

Red cells themselves have no immune function--but carrying oxygen and CO2 is enough! It is the white cells and the serum that have evolved to protect us from the pathogens. Their functions are complex but precise, and not subject to casual abuse or well-meaning but physiologically impossible interventions.

A lot of foodie folklore and quackery surrounds immunity ("EAT ZINC", "live on antioxidants", "boost your immune system with"...whatever). The immune system generally takes care of itself--and YOU--without a lot of help. Where genetic anomalies, catastrophic disease, or iatrogenesis (diseases caused by medical treatment, of which there are myriad) interfere the result can be disastrous, of course. But zinc is not going to help then.

The best care for the immune system is to maintain general good health. In addition, vaccination is a true medical miracle--far more significant than antibiotics--that everyone should take advantage of UNLESS SPECIFICALLY CONTRAINDICATED. A healthy immune system will not be "overwhelmed" by vaccines--just the opposite, in fact (to address just one immunity lie spread by know-nothings).

So, don't smoke or ingest toxins, get your shots, and leave the zinc supplements on the shelf (heavy metals are poisons, by the way....). Your blood is on the job.