Question

Young patients after an untreated throat infection with streptococci bacteria can develop rheumatic heart disease later in life. Studies have shown that the heart disease affects primarily the mitral valve whose surface cells have proteins similar to a surface protein common to many strains of streptococcal bacteria. Based solely on the information above, what class of disease best describes rheumatic heart disease? A. Congenital endocrine abnormality such as type I diabetes B. Hypersensitivity reaction such as an autoimmune disease C. Allergic reaction such as a bee sting D. Congenital structural abnormality of the heart such as a patent foramen ovale

Short answer

B. Hypersensitivity reaction such as an autoimmune disease

Step-by-step solution

Analyze the Condition

Understand that rheumatic heart disease develops after a throat infection with streptococci bacteria. This suggests that the disease is a reaction to an infection, not something someone is born with (congenital).

Identify the Target of the Disease

Note that rheumatic heart disease primarily affects the mitral valve. The disease results from surface proteins on the heart valve cells being similar to streptococcal bacteria proteins.

Understand the Mechanism

Identify that the similarity in proteins causes the immune system to mistakenly attack the mitral valve cells, suggesting an autoimmune response.

Match with Disease Types

Compare the description to the provided options. Since the disease is due to an autoimmune response (immune system attacking body's own cells), it fits with a hypersensitivity reaction much like other autoimmune diseases.

Eliminate Incorrect Options

Eliminate typical congenital diseases (options A and D) since they are present from birth, and allergic reactions (option C) since they are allergic responses to external substances. The correct type is best described by option B.

Key concepts

Autoimmune Disease

Rheumatic heart disease is a fantastic example of how an autoimmune disease works. In autoimmune diseases, the body's immune system mistakenly attacks its own tissues.

For example, in rheumatic heart disease, the immune system creates antibodies to fight streptococcal bacteria from a throat infection. Sometimes, these antibodies mistakenly target the heart’s mitral valve because of similar proteins.

Here are some key points to remember about autoimmune diseases:

• The body cannot distinguish between foreign invaders and its own cells.
• It mistakenly attacks its own tissues, causing inflammation and damage.
• Examples include Type 1 diabetes, multiple sclerosis, and lupus.

Rheumatic heart disease fits as an autoimmune disease because the immune system’s attack leads to inflammation and damage to the heart valves.

Hypersensitivity Reaction

A hypersensitivity reaction involves an exaggerated immune response to an antigen. There are four types of hypersensitivity reactions: I, II, III, and IV.

Rheumatic heart disease is an example of Type II hypersensitivity. The immune system creates antibodies against the streptococcal bacteria, but these antibodies cross-react with heart tissue.

Important aspects of hypersensitivity reactions include:

• Type I is an immediate reaction, like anaphylaxis.
• Type II involves antibody-mediated destruction, as seen in rheumatic heart disease.
• Type III is due to immune complexes, like in systemic lupus.
• Type IV is a delayed reaction, such as in tuberculosis skin tests.

In rheumatic heart disease, the antibody response leads to chronic damage and inflammation of the heart valves.

Streptococcal Bacteria

Streptococcal bacteria are a common cause of throat infections. If untreated, they can lead to severe complications like rheumatic fever, and eventually rheumatic heart disease.

Here are some key points about streptococcal bacteria:

• They are gram-positive bacteria.
• They commonly cause infections like strep throat and skin infections.
• Streptococcal pharyngitis can lead to rheumatic fever if untreated.
• Prevention includes timely treatment of strep infections with antibiotics.

The connection between streptococcal infections and rheumatic heart disease lies in the immune mimicry, where the immune system targets both the bacteria and the heart valve cells due to similar surface proteins.

Immune Response

The immune response is the body's defense against infections and harmful substances. It involves recognizing and attacking foreign invaders like bacteria and viruses.

When the immune system encounters streptococcal bacteria, it produces antibodies to fight the infection. However, in rheumatic heart disease, these antibodies can mistakenly target heart tissues, leading to an autoimmune reaction.

Key aspects of the immune response include:

• Recognizing antigens to neutralize or destroy pathogens.
• Producing antibodies specific to the infection.
• Memory for faster response to future infections.
• In some cases, mistaken attacks on the body’s own cells.

In rheumatic heart disease, the mistaken attack by the immune system causes inflammation and damage to the heart valves, illustrating a malfunction in the immune response.