Immunity to viruses

The infective life cycle of viruses

Infecting virus

Attachment to cell receptors

(tropism)

Penetration

Uncoating

Replication Synthesis of viral mRNA

Synthesis of viral proteins Synthesis of viral nucleic acids

Assembly Capsid formed

around nucleic acid

Release Lytic virus (no envelope) Budding virus (envelope)

Anti-viral effects of antibodies

• Antibody alone - blocks binding and entry to cells

• Antibody + complement - damage to enveloped viruses - opsonisation for phagocytosis

• Antibody bound to infected cells - antibody-dependent cellular cytotoxicity

Antigenic drift and shift in influenza virus

Strains of influenza A virus can be defined by the antigenic type of their capsid proteins – haemagglutinin (H) and neuraminidase (N).

H0N1

H3N2 H2N2

H1N1

(1933 – 1946)

(1968 – ) (1957 – 1967)

(1947 – 1956)

Innate and adaptive immunity to virus infected cells

Virus titre

Time after virus infection

Innate Adaptive

The anti-viral action of interferons

Type 1 interferons also enhance the expression of HLA class I proteins, and activate natural killer cells.

HLA class I

CD8+

Kill

Natural killer cell

(large granular

lymphocyte)

recognition of

infected target cells.

Formation of enveloped RNA virus

Virus glycoproteins

Host cell plasma membrane

Virus matrix proteins

Virus RNA

Virus formation

Virus budding

Virus release

(HLA class I expression is inhibited by a number of viruses, eg. adenovirus, cytomegalovirus, herpes simplex virus.)

Video can be viewed on YouTube

Title: T cell Attack

URL: http://www.youtube.com/watch?v=nL_VyrTR2r4

Target cell killing by a cytotoxic T cell

Killer cells also produce type 2 interferon (IFN-γ), that has anti-viral activity and enhances HLA class I and class II expression.