White+Blood+Cells+in+Lung+Produce+Histamine

George Caughey, MD Chief of Pulmonary/Critical Care Medicine San Francisco VA Medical Center January 2007

The study reported that histamine can be produced in large quantities by white blood cells in the lungs called Neutrophils. These white blood cells are the major component of pus, which is found in infection. The production of pus is a result of inflammation, which is a histamine-induced response.
 * Abstract:**

The study was performed on mice, and illustrated that lung neutrophils are able to produce significant amounts of histamine. Prior to this research, it was believed that the main source of histamine in our lungs was mast cells. Now that researchers know that white blood cells have the ability to produce large quantities of histamine, we can look at respiratory infection and allergy as being more closely linked.


 * How Did They Prove That Histamine is Produced by WBC's in the Lungs?**

Dr. Caughy and his team "hypothesized that an infection in the airway would release histamine from mast cells."

Two groups of mice were assembled; one population of mice possessed a genetic abnormality that caused then to lack all mast cells. The other group were normal wild mice. Both groups were exposed to mycoplasma (the bacterium that can cause pneumonia). Both of the groups of mice developed pneumonia.

The researchers expected the abnormal mice to do better thank the wild mice, as the infection would not be able to provoke mast cells to release histamine. Instead, the abnormal mice that lacked mast cells actually experience histamine levels that "rose up to 50 times normal." This meant that something other than mast cells were able to produce histamine in the lungs.

While their hypothesis was correct, and infection in mice with mast cells did cause mast cells to release histamine, the abnormal group of mice actually presented the researchers with the information they were looking for. Neutrophil numbers increased in the abnormal mice, and those neutrophils produced large amounts of histamine; the mycoplasma bacteria "induced neutrophils to produce the enzyme that produces histamine." (The enzyme is histidine decarboxylase. (Simons)) While neutrophils individually produce only small quantities of histamine, the pus produced from infection contain billions of neutrophils, which highly increase histamine production. (Caughey)

The wild mice suffered less severe infection because their mast cells were able to protect them against bacteria.

Antihistamines were then used to drop the histamine levels in the abnormal mice. As the histamine level dropped, the severity of the pneumonia also declined, proving that antihistamines might be a helpful therapy for those suffering from lung and airway infection.

The presence of histamine in our bodies serve to tell us that something is wrong. Our mast cells release histamine, so we often try to block them with antihistamines. While we block the histamine receptors, we still need the mast cells! They protect us even though they release histamines which might bother us. Studies such as this one show us that our bodies have backup methods for releasing histamine during infection. The response is intended to protect us from invaders (in his case, the invader was a bacterium that induces pneumonia), but sometimes chemical mediators can further hinder our immune systems instead of making us better. Studies such as this show that histamine can be closely linked to bacterial infection, and that antihistamines might serve as a helpful therapy for treating respiratory infection. (Caughey) **
 * What This Reveals About Histamine: