Question

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Classify the statements as being true for either endotoxins or exotoxins. Exotoxins Endotoxins Composed of lipid A Cannot be used in a toxoid vaccine Can be highly specific Part of cell structure Unaffected by heat May cause cell lysis Activate B cells May hydrolyze phospholipids May activate helper T May cause fever and shock Neutralized by antitoxin Can be used in a toxoid vaccine Reset

Answer 1

The following statements are true for exotoxins:

May cause cell lysis as it causes disruption of normal metabolism of cell whereas endotoxins are released during the lysis of the cells.

Exotoxins may hydrolyze phospholipids as it forms pore after binding to the cellular membrane through which lysis of the cell takes place.

Exotoxins are neutralized by antitoxin as antitoxin antibodies bind to the exotoxin molecule and thus prevent it from interacting with host target cells.

Exotoxins may activate helper T-cells and may cause fever and shock. These are its toxic effects.

Exotoxins can be highly specific and can be inactivated by means of heat or by treating it chemically, thus can be used in a toxoid vaccine.

The following statements are true for endotoxins

Endotoxins are a part of the cell wall of gram-negative bacteria and are lipopolysaccharide in nature. Therefore, have a lipid component Lipid A and a polysaccharide component.Hence the statement which says endotoxins are composed of lipid A is true and they are part of cell structure too.

Since they are lipopolysaccharide in nature, they are unaffected by heat.

Although endotoxins are antigenic, yet they cannot be used in a toxoid vaccine.

Endotoxins activate B cells as they act as B cell mitogens and stimulate the differentiation and multiplication of B cells.

Endotoxins

Made by gram - negative cells only

Unaffected by heat

Component of outer cell membrane

Lipopolysaccharide in nature

Not very potent , unless systemic.

Exotoxin

Produced by gram - positive and gram -negative bacteria

Denatured by heat

Synthesized in cytoplasm,sometimes secreted

Protein in nature

Mostly very potent