immune response to microbes

7/28/2019 Immune Response to Microbes

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IMMUNE RESPONSE TO

MICROBES


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Protective Immunity To Microorganisms

Defense against microbes is mediated by:

Innate immunity and acquired immunity

Humoral immunity (antibodies)

Through both

Cell mediated immunity (CMI)


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Defenses Against Bacteria-EXTRACELLUAR BACTERIA

The innate immunity:

1. Complement activation

2. Phagocytosis

3. The inflammatory responseCOMPLEMENT P ACTIVATE

Make membrane attack complex

kill bacteria1. Inflammation: + recruit phagocytes, B & T lymphocytes

2. (Acquired response antibodies, cytotoxic Ts if needed)


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Figure 24-17: Immune responses to bacteria

Complement P Activates


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The acquired immune responses:

1. The humoral mechanisms (antibodies) main role2. Cell mediated immune response less role

Antibodies induce immunity through:

1. Neutralization of bacterial toxins2. Antibodies attach to the surface of bacteria and;

Act as opsonins, enhance phagocytosis (Opsonization)

Prevent adherence of bacteria to their target cells

e.g. IgA on mucosal surfaces Activation the complement leading to bacterial lysis

Agglutinate bacteria, preventing their spread and

facilitating phagocytosis



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Cell mediated immune mechanisms:

* Microbes are internalized by APCs and presented to TH

* TH cells are activated and release cytokines which;

-Activate phagocytosis their microbicidal functions

- Stimulate antibody production

- Induce local inflammation



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1) Innate immunity

It is mainly by natural killer (NK) cells- They kill infected cells and secrete IFN-

- IFN-activate phagocytosis to kill intracellular microbe

E.g. tuberculosis, leprosy, listeriosos

2) Acquired immunity is mainly by CMI

-Activation of macrophages to kill intracellular microbes- Lysis of infected cells by cytotoxic cells (CTLs)

- Most of these organisms are resistant to phagocytosis, cause

chronic infection and granuloma formation

Defenses Against Bacteria-INTRACELLUAR BACTERIA


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1. Virus neutralization

* In viremic infectionsAntibodies neutralize virus, preventing its attachment to

receptor sites on susceptible cells e.g. poliovirus, mumps,

measles, rubella

* In superficial non-viremic infections (influenza) Secretory IgA

neutralizes virus infectivity at the mucous surfaces

Defenses Against - VIRAL (Humoral Immunity)

2. Antibodies destroy free virus particles directly:

i- Aggregation of virus and opsonization

ii- Complement mediated lysis


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Cell mediated cytotoxicity, mediated by :

- Cytotoxic T-cells (CTLs)

- NK cells

- Activated macrophages

Defenses Against - VIRAL

(Cell Mediated Immunity)


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Anti-viral activity of interferons (IFNs)

- INF-inhibit intracellular replication of viruses

- IFN-activate NK-cells to kill virus infected cells

- IFNs have no direct effect on extracellular virus

- IFNs act early in viral diseases before antibody

- INFs activity is not specific

Defenses Against - VIRAL (IFNs)


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Defenses Against Viral


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Immune response to fungi consist mainly of :

1) Innate immunity is mediated by:

- Neutrophils and macrophages

- Fungi are readily eliminated by phagocytes

2) Acquired immunity (cell mediated immunity)

- CMI acts in a manner similar to its action againstintracellular bacteria

* Disseminated fungal infection are seen in: immunodifcient persons

Defenses Against - FUNGI


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TERIMAKASIH

immune response to microbes

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