Question

1. The causative agent for elephantiasis is the roundworm Wuchereria bancrofti which is an example of a(n) ___________________?

2. 		protozoan
   		alga
   		helminth
   		none of these

1. In an A-B exotoxin, which component binds to a receptor on the host cell?

   		the A component
   		the B component

1. Which of these cell types are not immunologically specific?

2. 		B cell
   		T helper cell
   		natural killer (NK) cells
   		all of these are correct

1. Lysozymes _________.  

   		destroy bacterial cell walls
   		are found in tears
   		are found perspiration
   		all these are correct

1. Innate immunity ______________.

		is always slower than adaptive immunity in responding to pathogens
		is nonspecific and present at birth
		involves a memory component
		involves T cells and B cells

1. Regarding the complement system, which of these is a possible result?

		cytolysis
		inflammation
		opsonization
		all these are correct

1. Which of these is true about the structure of antibodies?

   		they have 2 heavy chains and 2 light chains
   		they have constant regions (C) and variable regions (V)
   		chains are linked together by disulfide bridges
   		all of these are correct

1. Which of the following is not one of Koch’s postulates?

		same pathogen must be present in every case of the disease
		the pathogen must be isolated from the diseased host and grown in pure culture
		the isolated pathogen must cause the disease when it is inoculated into a healthy, susceptible laboratory animal
		all of these represent one of Koch’s postulates

Answer 1

Wuchereria bancrofti is a parasitic worm causing diseases like filariasis by affecting the lymphatic system of humans. It belongs to the phylum Nematoda which along with the phylum Cestoda and Trematoda form the major class of Helminth parasites. Hence, it is a helminth parasite.

A-B exotoxins are secreted by pathogens that infects the cells of the hosts. The two components A and B have two different activities. The A site is the Active site which contains the toxic enzymes that are responsible for affecting the cell by inducing or repressing any of it's gene expression. The B component is the binding site that binds to the host cell receptors. So the correct answer is B component.

Natural Killer cells (NK cells) bind to different infected cells or tumors and they are not specific to a single antigen. They destroy the cells by producing a substance called perforin. They are non specific immune cells and have wide range of pathological activity whereas the B cells and T cells are specific in nature and contribute to adaptive immunity. So the correct answer is NK cells.

Lysozyme is a natural anti microbial enzyme which can destroy bacterial cells by acting upon their cell walls. It is present in bodily secretions. It is neutral in pH, found in nasal secretions and also gastric releases. It is seen in sweat, mucous, saliva and also tears. Hence, all the options are correct.

Innate immunity is present in an individual from birth and they are the 1st line of defense against pathogens. It involves mast cells, dendritic cells, NK cells and macrophages. Innate immunity comprises of barriers like the mucous membranes and skin that trap pathogens that try to enter our body. It does not have any memory and is non specific i.e., it cannot recognize any pathogen as specific. And as it encounters the pathogen 1st it is quick in response. So the correct answer is it is non specific and present at birth.

Complement system is part of our immune system which is a set of proteins that help enhance the immune response towards an antigen or any infected cell. They help in opsonization which is the activation of neutrophils and macrophages that engulf the pathogens. They also help in inflammation by activating the mast cells and basophils which release histamine and serotonin inducing inflammatory response. Also lysis of bacterial cell is mediated by some of the proteins of the complement system. Therefore, all of them are correct.

Antibody is a small protein molecule secreted by the plasma cells. They are Y shaped structures and have two light chains of 25kDa each that are attached to two heavy chains of 50kDa each with the help of disulphide bonds. They have variable regions on both heavy and light chains that bind to the antigens and there are constant regions that perform only biological activity. So all the given options are correct.

All of them represent Koch's postulates. They were given by Robert Koch to identify any causative organism of a particular disease. Total 4 postulates were given. Apart from the 3 options given here there is another postulate that states that the causative organism when resiolated from the laboratory animal should be identical to the original pathogen isolated from the diseased animal outside the lab.