Question

1. Gonococci has two outer structures that show high antigenic variation. What are they? Also choose one briefly explain how it shows antigenic variation.

Answer 1

Answer: Pilli (made up of different pillin proteins) and Outer membrane protein (OMP) are the structure which is responsible for the antigenic variation.The antigenic variation is generally shown by a special mechanism called as Gene Switching found in Gonococci .

Explanation: Pathogenesity begins with the

1.entry to host body

2. Adhesion to host cell

3. propagation

4. destruction

5. Growth

Goanococci is envaded to host cell by sexual transmission. But for the process of adhesion this organism do some important modification for propagation of pathogen to host cell. For the process of adhesion they uses the pilli protein and for the propagation they uses pilli + some outer membrane protein.

Pilli : pilli is an extention of cytoplasm which is made up of different pillin proteins. This pillin protein are made up of different amino acids. This pilli is antigenic in nature which helt the pathogen in two ways:

a) help to escape from host immunity

b) attaching to cell surface of host

As we know that for any gene to be active it must require the promoter sequence for the process of transcription and translation.But the some pilli proteins do not have the promoter sequences just before the gene. so this causes  problem for the host immune cell to detect and kill that protein by complement activation pathway.

It can be clearified by an example as suppose if a pathogen is having three gene as A, B and C . so if the promoter is present just before the gene C as it is going to invade the host cell it can be killed due to antigen detection mechanism of immunity. But from escaping this immune detection the neisseria uses a special type of Gene Switching mechanism where they use to replace the gene position so as to escape from host immunity. As here we know that some gene (A and B) do not have promoter so the immune system can only detect the C gene. Here by the replacement of gene position as (placing gene A in place of C ) just after the promoter will be confusing for host immune system to identify it as different gene. Hence it can escape from host immunity.

Outer membrane protein (OMP)= There are several types of protein as TYPE I, II,III .

Type I which act as porin complex so help bacteria to envade the host tissue.

Type II can also go through antigenic variation to invade host immune system because OMP II can vary along or throughout the time to generate different diverse nature of different type of antigen(due to different type gene switching) so as to escape from immunity.

Inspite of this they also contain Lipo-oligosaccharides(LOS) which is the unique feature of gonococcus. This is generally shorter, more highly branched and consists of non repeat sequences.In this a special type of O antigen is present which is a kind of endotoxin. The main characteristics of this endotoxin is that it is heat resistant so this character of pathogen is also making the entry easy inside the host cell.