I once wrote a research paper for Immunology on nicotine. Wasn't long, but I'm gonna throw out a few things I learned about nicotine...

Nicotine Addiction

The less nicotine a cigarette contains, the more cigarettes a person will smoke in a day. In one study by London’s Central Middlesex Hospital, it was concluded that in situations where the supply of cigarettes is limited, a smoker would smoke the cigarette and leave the butt much shorter than the smoker normally would. Yet another study by Harvard Medical School concluded that when nicotine content in a cigarette was low, the test subjects would unconsciously hold the smoke in their lungs for a longer period of time than normal.

Nicotine impairs your breathing.

When cigarette smoke is inhaled, nicotine acts as a stimulant. It will actually speed up a person’s heart and central nervous system. The heart speeds up, blood vessels constrict, and the blood pressure increases. Therefore, less blood and oxygen can move throughout a smoker’s body. After about 10 to 19 minutes, the blood nicotine concentration of a smoker is around 15 nanograms per milliliter. The average intake of nicotine per cigarette is 1 mg, but it can vary from .5 mg to 3 mg. The elimination half-life of nicotine is 2 to 3 hours

Nicotine and Your Brain

When nicotine finally reaches the brain, it binds to dopamine receptors. The activation is exploited by most drugs used for pleasure. The reaction leads to addiction, and as the brain absorbs nicotine molecules, it becomes tolerant to nicotine. The tolerance fades quickly, though, and disappears overnight. This explains why, according to smokers, the first smoke of the morning is always more pleasurable than others. Tests conducted by Yale Medical School have pinpointed the actual receptor on a dopamine cell that nicotine will bind to. However, when the specific protein receptor was blocked, the mice could still create the dopamine-releasing effect with other illegal drugs such as cocaine, proving that different addictive drugs have different pathways into the dopamine cells.

Nicotine can make your lungs more vulnerable to infection.

The Department of Medical Microbiology and Immunology at the University of South Florida College of Medicine discovered one effect of nicotine on alveolar macrophages. Although the effect of nicotine on the lungs and alveolar macrophages is still poorly understood, they managed to reveal some new information. They first infected macrophages with Legionella pneumophila, a causative agent for pneumonia. Then, they treated the macrophages with nicotine. The nicotine significantly enhanced the replication of the bacteria. The research concluded that nicotinic acetylcholine receptors are a part of the regulation of alveolar macrophages and can contribute to cigarette-related risk factors for respiratory infections.

Nicotine can kill your Immune System.

Researchers at the Lovelace Institutes published an article in the Journal of Immunology that found new evidence that nicotine, at least in mice, can modify T cell activation so that the T cells, though having normal background levels of some chemicals related to activation, will fall into a state of anergy (*note: anergy is like a phase in which a cell does nothing). This leads to cigarette-induced immunosuppression. The same researchers had already proven that cigarette smoke inhibited antibody responses to both T-dependent and T-independent antigens. They believed that the effects of nicotine on cell signaling caused the inhibition. Their conclusion was that partial activation by nicotine is a general mechanism for the induction of T cell tolerance.

Works Cited

Institute of Medicine. Growing Up Tobacco Free. Washington, D.C.: National Academy Press, 1994. p. 36-37
Swan, Neil. Like Other Drugs of Abuse, Nicotine Disrupts the Brain's Pleasure Circuit. http://www.nida.nih.gov/NIDA_Notes/NNVol13N3/Nicotine.html The National Institute on Drug Abuse Notes section. Accessed Sunday, May 12, 2002.
Matsunaga, Kazuto, et al. Involvement of Nicotinic Acetylcholine Receptors in Suppression of Antimicrobial Activity and Cytokine Responses of Alveolar Macrophages to Legionella pneumophila Infection by Nicotine. http://www.jimmunol.org/cgi/content/abstract/167/11/6518 The Journal of Immunology archives. Accessed Sunday, May 12, 2002.
7. Geng, Yuemei, et al. Effects of Nicotine on the Immune Response. The Journal of Immunology, 1996, edition 156: p. 2384-2390.

And, as usual, if you find any incorrect information in this report, please msg me and tell me. If I made any errors, I'd like to know.