Every academic specialty has its unique jargon. On Saturday, Professor Eisenbarth pointed out that the field of Immunology is no different. She generously proceeded to simplify and deconstruct some of the jargon for us: those who stuck with us through various scheduling changes of this cafe would confirm that waiting indeed has its rewards!
The complexity of the nervous system that is made up of billions of cells is well recognized; the immune system on the other hand, working with a fraction of the cells in the nervous system, works assiduously to keep you healthy. But despite your best efforts, sometimes you fall sick. It’s because your immune system has recognized a breach and is mounting an attack against the invader. This can happen when you encounter the flu virus, or perhaps eat some outdated food infested with bacteria or mold. Once the invasion is quelled, the system thrums back to a healthy rhythm.
Top: The immune network. Center: Major cell types in the immune system. Bottom: An allergic response (adapted from CDC and NIH sites)
The immune system is made up of a network of organs which have a variety of cells coursing through them, each with a unique function and a unique way to communicate with other cells. Some of these cells work day and night patrolling your body, making sure foreign entities are swiftly dealt with. Most of this happens unbeknownst to you through the innate immune system, and assaults are typically mounted and completed within hours. It’s a relatively nonspecific process and pathogens are annihilated at or near the point of entry: skin, mucous membranes of the respiratory, digestive, and reproductive tracts.
The other arm of the immune system is the adaptive immune system, and it’s this arm that is also involved in allergic reactions. Allergic reactions belong to one class of immune responses that are exaggerated reactions, or hypersensitivity. In one of many possible scenarios that result in an allergic reaction, when dendritic cells (DC) encounter an innocuous foreign protein, e.g., peanut protein, a cascade is initiated that includes recruiting T-lymphocytes, which mobilize and influence B-lymphocytes to quickly secrete unique antibodies to the innocuous foreign protein. These antibody (IgE) molecules attach to the surface of mast cells. This attachment initiates the release of histamine and other molecules, the concentration of which can determine the gravity of the allergic reaction (which is why you can take Benadryl, an anti-histamine, for relatively mild allergic reactions). The first time this encounter occurs in a susceptible individual, the end result is usually harmless and can often go undetected. Subsequent exposure to the allergen results in a robust response that can be as minor as a rash, to as profound as anaphylaxis, which left untreated can lead to death.
Unfortunately, food intolerance/sensitivity is often confused with food allergies, because some of the symptoms overlap. However, while the allergies occur via the adaptive immune system, food intolerance is typically limited to digestive problems. Often, food intolerance can occur due to the absence of particular digestive enzymes, as in an intolerance to milk: the absence of the enzyme lactase makes it impossible to digest lactose, the sugar in milk; the normal bacteria in the intestine though, have a field day digesting that lactose, and in the process cause you digestive problems. While celiac disease is not an allergy, it does involve the immune system – in presence of gluten, the body mounts an autoimmune response and destroys the intestinal lining. Unlike celiac disease, gluten intolerance/sensitivity does not damage the small intestine. Celiac disease is genetic, but not everyone who carries the genetic signature for it will react adversely to gluten. Perhaps a prominent characteristic distinguishing celiac disease from allergies is that accidentally consuming foods containing gluten will not cause anaphylaxis, as can happen with allergies.
There are many hypotheses for why there appears to be a recent spike in the number of people who have allergies – some have a scientific basis, others are insubstantial. Allergies tend to run in families, although the severity is not necessarily consistent. The role of environmental factors in tilting the balance towards allergies has also been considered, which has led to the hygiene hypothesis – that an excessively clean environment in early childhood can suppress natural development of the immune system, leading to a pronounced tendency to allergies. Based on just these two possibilities – genetic contribution, and environmental influence – one can appreciate the complexity of this field of research. Summarizing it is a daunting task, which is why this email might sound complicated and incomplete. But do watch the cafe video, because Stephanie Eisenbarth simplified it significantly for us!