Complement System MCQ Quiz

The membrane attack complex in the complement pathway consists of C5b, C6, C7, C8, and C9. These proteins work together to form a pore in the membrane of target cells, leading to cell lysis. C5b initiates the complex formation, followed by the recruitment of C6, C7, C8, and finally C9. This complex formation is an important defense mechanism of the immune system against pathogens.

The complex formed by complement components C5b,6,7,8,9 is known as the membrane attack complex (MAC). Its main function is to perforate bacterial cell membranes, leading to cell lysis and destruction. This is an important defense mechanism of the immune system against bacterial infections. The MAC creates pores in the bacterial cell membrane, causing the leakage of intracellular contents and ultimately leading to the death of the bacterium. This function is crucial in eliminating bacterial pathogens from the body and preventing the spread of infection.

C5a is the most potent complement component in attracting neutrophils to the site of infection. It acts as a chemokine, which is a type of signaling molecule that attracts immune cells to the site of inflammation or infection. C5a specifically attracts neutrophils, which are a type of white blood cell that plays a crucial role in the immune response against bacterial infections. By attracting neutrophils to the site of infection, C5a helps to enhance the immune response and promote the clearance of pathogens.

C1q is the initial complement component that is bound by complement-fixing antibodies. Complement-fixing antibodies can activate the complement system, and C1q is the first component that binds to the antibodies, initiating the complement cascade. C1q then recruits other complement components, leading to the formation of the membrane attack complex and the destruction of target cells. C1s and C3b are also components of the complement system, but they are not the initial complement component bound by complement-fixing antibodies. Therefore, the correct answer is C1q.

C3b is the most important opsonin among the given complement components. Opsonins are molecules that enhance the process of phagocytosis, which is the engulfment and destruction of pathogens by immune cells. C3b is a key opsonin as it binds to the surface of pathogens, marking them for recognition and ingestion by phagocytes. This enhances the efficiency of the immune response by promoting the removal of pathogens from the body.

The question asks for several complement components, and the correct answer is "Enzymes." Complement components are a group of proteins that are part of the immune system and help to enhance the body's immune response. Enzymes are one of the main types of complement components, along with antibodies and hormones. Therefore, "Enzymes" is a valid answer to the question.

C3 is cleaved by the complement components C3b and Bb to form C3bBb. This cleavage is part of the complement system, a group of proteins that play a crucial role in the immune response by promoting inflammation, opsonization, and cell lysis. C3bBb is an important component of the alternative pathway of complement activation, which provides an early defense against pathogens. It acts as a C3 convertase, leading to the amplification of the complement cascade and the generation of more C3b molecules.

A deficiency of C5b,6,7,8,9 predisposes to bacteremia caused by members of the genus Neisseria because these complement components are involved in the formation of the membrane attack complex (MAC). The MAC is responsible for directly killing bacteria by creating pores in their cell membranes. Without a functional MAC, bacteria are able to evade the immune system and cause infection.

The alternative pathway of complement is considered the first line of defense against microorganisms, as it can be activated directly by the presence of certain microorganisms, such as bacteria, viruses, and fungi. On the other hand, the classic pathway of complement requires the presence of specific antibodies to be activated. Therefore, in the initial exposure to a microorganism, the alternative pathway is more likely to be activated before the classic pathway.

The patient's symptoms of swellings on her arms and legs, feeling of fullness in her throat, and difficulty breathing are consistent with angioedema. Angioedema can be caused by a complement abnormality, specifically a deficiency of C1 inhibitor. C1 inhibitor is responsible for regulating the activation of the complement system, and a deficiency can lead to uncontrolled activation of complement proteins, resulting in angioedema. Therefore, the most likely explanation for the patient's condition is that she has too little C1 inhibitor.