What causes allergies?

To help answer this question, let’s look at a common household example. A few months after the new cat arrives in the house, dad begins to have itchy eyes and episodes of sneezing. One of the three children develops coughing and wheezing, especially when the cat comes into her bedroom. The mom and the other two children experience no reaction whatsoever to the presence of the cat. How can we explain this?

The immune system is the body’s organized defense mechanism against foreign invaders, particularly infections. Its job is to recognize and react to these foreign substances, which are called antigens. Antigens are substances that are capable of causing the production of antibodies. Antigens may or may not lead to an allergic reaction. Allergens are certain antigens that cause an allergic reaction and the production of IgE.

The aim of the immune system is to mobilize its forces at the site of invasion and destroy the enemy. One of the ways it does this is to create protective proteins called antibodies that are specifically targeted against particular foreign substances. These antibodies, or immunoglobulins (IgG, IgM, IgA, IgD), are protective and help destroy a foreign particle by attaching to its surface, thereby making it easier for other immune cells to destroy it. The allergic person however, develops a specific type of antibody called immunoglobulin E, or IgE, in response to certain normally harmless foreign substances, such as cat dander. To summarize, immunoglobulins are a group of protein molecules that act as antibodies. There are five different types; IgA, IgM, IgG, IgD, and IgE. IgE is the allergy antibody.

(In 1967, the husband and wife team of Kimishige and Teriko Ishizaka detected a previously unrecognized type of immunoglobulin in allergic people. They called it gamma E globulin or IgE.)

In the pet cat example, the dad and the youngest daughter developed IgE antibodies in large amounts that were targeted against the cat allergen, the cat dander. The dad and daughter are now sensitized or prone to develop allergic reactions on subsequent and repeated exposures to cat allergen. Typically, there is a period of “sensitization” ranging from months to years prior to an allergic reaction. Although it might occasionally appear that an allergic reaction has occurred on the first exposure to the allergen, there must have been a prior contact in order for the immune system to be poised to react in this way.

IgE is an antibody that all of us have in small amounts. Allergic persons, however, produce IgE in large quantities. Normally, this antibody is important in protecting us from parasites, but not from cat dander or other allergens. During the sensitization period, cat dander IgE is being overproduced and coats certain potentially explosive cells that contain chemicals. These cells are capable of causing an allergic reaction on subsequent exposures to the dander. This is because the reaction of the cat dander with the dander IgE irritates the cells and leads to the release of various chemicals, including histamine. These chemicals, in turn, cause inflammation and the typical allergic symptoms. This is how the immune system becomes exaggerated and primed to cause an allergic reaction when stimulated by an allergen.

On exposure to cat dander, the mom and the other two children produce other classes of antibodies, none of which cause allergic reactions. In these non-allergic members of the family, the dander particles are eliminated uneventfully by the immune system and the cat has no effect on them.

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Discrimination May Lead to Smoking in Boys

FRIDAY, Jan. 22 (HealthDay News) — Minority teen boys smoke more when they suffer discrimination, but that’s not the case for minority teen girls, a U.S. study finds.

Perceived discrimination had no effect on smoking rates among minority girls aged 12 to 15 and was associated with lower rates of smoking among minority teen girls aged 16 to 19.

“Our findings in girls, especially in the older girls, really surprised us,” study first author Dr. Sarah Wiehe, an assistant professor of pediatrics at the Indiana University School of Medicine, said in a news release from the school. “We do not know why older girls who perceived discrimination were less likely to smoke, but there may be a possibility that they perceived discrimination because they were pregnant and also that they did not smoke due to pregnancy.”

The study included 2,561 black and Hispanic teens, aged 12 to 19, living in low-income households in Baltimore, Boston, Chicago, Los Angeles and New York. About 25% of the teens reported discrimination within the previous six months, and 12% said they’d smoked within the previous 30 days.

Increased smoking by boys who suffer higher levels of discrimination may be caused by increased stress from male-specific targeting by police and business, the study concluded.

“Boys and girls may experience discrimination differently due to where they spend their time and that may account for the differences in whether discrimination was associated with smoking,” Wiehe said. “In other words, the context of discrimination matters. We need to be aware that discrimination is a public health problem for adolescents — one related to major health issues like smoking — and need to actively work to reduce these occurrences.”

The study appears online and in the March print issue of the American Journal of Public Health