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Host Defenses Againts Viral

Infection

erly

Objectives

Describe three mechanisms of

immune responses to viral infection.

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Human are protected from viral infection by:1. Natural barriers

2. Non spesific immune defenses

3. Antigen-spesific immune responses

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The ultimate goal of the immune response

to eliminate . The virus

. The cells harboring

. Replicating the virus

The immune responsethe best of

controlling a virus infection Humoral and cellular immune responses are

important for antiviral immunity

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Non spesific Immune Defenses

Fever and body temp

Infected cells and macrophages

- IFN

- other cytokine

MN Phagocyte system

NK cellls

Local rapid response to viral infection

Activated the spesific immune responses

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IFNtrigger local and systemic responses

Fever can limit the replication viruses

MN Phagocyte

phagocytize virus and celldebris

Kuppfers cells and spleenrapidly clear

many viruses from the blood

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Antibody and Complemenopsonization

Macrophages present antigen to T cell

IL1&IFNinitiate the antigen spesific immune

response

NK cellsto kill viral-infected cells

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Biological Effects of IFN

Inhibition of multiplication of viruses

Inhibition of cell division

Immunomodulation Increased MHC antigens & Fc receptors

NK cellActivation and maturation

T cellProliferation ,suppressed lymphokinerelease

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DTH(CD4)modulation of DTH

CTL(CD8)cytotoxicity

Macrophage

activation

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Antigen-Spesific Immunity

Humoral and CMIplay different roles in

resolving viral infection

Antibodyact mainly on extracellular virions

CMIdirected at the virus-producing cells

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Antibodyblock the progression of disease

by: netralization&opsonization of cell-free

virus

- binding viral attachment proteins

- preventing interaction with target cells

- destabilizing the virus

- degradation

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Antiviral role of antibodypreventing a viremia

Antibody most effective at resolving cytolytic

infections.

Resolution occure because:

- The virus kills the cell factory and

- Antibody eliminate the extracellular virus

Antibody is the primary defense initiated by

vaccination

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T-cell Immunity

Promote Antibody ,inflamatory responses

and kills infected cells

CMI.- especially important for resolving infections

by: . Syncytia-forming viruses

. Non cytolytic viruses

. Controlling latent viruses

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Viral: - strain

- infectious dose- route of entry

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Viral Immunopathogenesis

Flu-like symptoms (IFN)

DTH and inflamation(T cell)

Immune-complex disease Hemorrhagic disease

Post infection cytolysis

Immunosuppression

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1.Medical Mcrobiology

2. Medical Microbiology and Immunology