Immune Response To Microbes 334x51

IMMUNE RESPONSE TO MICROBES

Protective Immunity To Microorganisms Defense against microbes is mediated by: Innate immunity and acquired immunity

Humoral immunity (antibodies) Through both Cell mediated immunity (CMI)

Defenses Against Bacteria-EXTRACELLUAR BACTERIA The innate immunity: 1. Complement activation 2. Phagocytosis 3. The inflammatory response COMPLEMENT P ACTIVATE Make membrane attack complex  kill bacteria 1. Inflammation: + recruit phagocytes, B & T lymphocytes 2. (Acquired response  antibodies, cytotoxic Ts … if needed)

Complement P Activates

Figure 24-17: Immune responses to bacteria

Defenses Against Bacteria-EXTRACELLUAR BACTERIA The acquired immune responses: 1. The humoral mechanisms (antibodies) “main role” 2. Cell mediated immune response “less role” Antibodies induce immunity through: 1. Neutralization of bacterial toxins 2. 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

Defenses Against Bacteria-EXTRACELLUAR BACTERIA 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

Defenses Against Bacteria-INTRACELLUAR BACTERIA 1) Innate immunity It is mainly by natural killer (NK) cells - They kill infected cells and secrete IFN-γ - IFN-γ 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 - VIRAL (Humoral Immunity) 1. Virus neutralization * In viremic infections Antibodies 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 2. Antibodies destroy free virus particles directly: i- Aggregation of virus and opsonization ii- Complement mediated lysis

Defenses Against - VIRAL (Cell Mediated Immunity) Cell mediated cytotoxicity, mediated by :

- Cytotoxic T-cells (CTLs) - NK cells - Activated macrophages

Defenses Against - VIRAL (IFNs) Anti-viral activity of interferons (IFNs) - INF-α inhibit intracellular replication of viruses - IFN-α 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

Defenses Against - FUNGI 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 against intracellular bacteria * Disseminated fungal infection are seen in: immunodifcient persons

TERIMAKASIH