The two β pleated sheets in each domain are held together by hydrophobic interactions and the conserved disulfide bond.  The three loops of each variable domain show considerable variation in length and amino acid sequence; these hyper variable regions  make up the antigen-binding site. 

TLS Online TPP Program

#Id: 9938

#Unit 4. Cell Communication and Cell Signaling

Host immune responses and bacterial evasion mechanisms

TLS Online TPP Program

#Id: 9939

#Unit 4. Cell Communication and Cell Signaling

Tuberculosis

Tuberculosis, caused by Mycobacterium tuberculosis.

Pulmonary infection usually results from inhalation of small droplets of respiratory secretions containing a few bacilli.

TLS Online TPP Program

#Id: 9940

#Unit 4. Cell Communication and Cell Signaling

The inhaled bacilli are ingested by alveolar macrophages in the lung and inhibiting formation of phagolysosomes

CD4+ T cells are activated within 2 to 6 weeks after infection.

TLS Online TPP Program

#Id: 9941

#Unit 4. Cell Communication and Cell Signaling

These cells wall off the organism inside a granuloma called a tubercle. The localized concentrations of lysosomal enzymes in these granulomas can cause extensive tissue necrosis.

TLS Online TPP Program

#Id: 9942

#Unit 4. Cell Communication and Cell Signaling

Diphtheria

Natural infection with C. diphtheriae occurs only in humans and is spread by respiratory droplets. 

The organism colonizes the nasopharyngeal tract and causes little tissue damage, with only a mild inflammatory reaction. 

TLS Online TPP Program

#Id: 9943

#Unit 4. Cell Communication and Cell Signaling

Virulence is due to its potent exotoxin, which destroys the underlying tissue and results in heart, liver, and kidney damage, as well as to suffocation following formation of a tough fibrous membrane in the respiratory tract