Immunity to Microbes
Fadel Muhammad Garishah
Infection and Immunity
Faculty of Medicine Diponegoro University
How do you describe this?
• Defense against microbes via innate and adaptive
• Responds in distinct and specialized ways to
different types of microbes
• survival and pathogenicity of microbes influenced
by the ability of the microbes to evade or resist
• tissue injury and disease may be caused by the
host response to the microbe and its products
rather than by the microbe itself.
The extracellular bacteria
• Extracellular bacteria defined as the bacteria
that capable to replicate outside the host
cells, e.g. in blood, connective tissue,
• The bacteria may either 1) induce
inflammation or 2) produce toxins that
destruct the body tissue
• E.g. of toxin: Endotoxin of gram-negative or
Innate immunity to extracellular
• Principles: complement activation,
phagocytosis and inflammatory response.
• Complement activation
• Activation of phagocytes and inflammatory
Adaptive immunity to extracellular
• Humoral immunity: block infection, eliminate
microbes and neutralize toxins
• CD4+ produces cytokines that induce local
inflammation and activate phagocytic function
and microbicidal activities of Macrophages
Polyclonal activation of T cells by
Extracellular bacteria evasion
• A mechanism used by bacteria to evade
• Genetic variation of surface antigen (E. coli, N.
gonorrhoeae, S. typhimurium)
• Resistance to phagocytes (Pneumococcus)
• Destruction to ROS (Catalase producing
Innate and Adaptive Immunity
• The innate immune response to intracellular
bacteria consists mainly of phagocytes and NK
(natural killer) cells.
• The major adaptive-protective immune
response against intracellular bacteria is cell-
• The macrophage activation in response to
intracellular microbes is capable of causing
Figure 15-5 Naive CD4+ T lymphocytes may differentiate into TH1 cells, which activate
phagocytes to kill ingested microbes, and TH2 cells, which inhibit macrophage activation.
The balance between these two subsets may influence the outcome of infections, as
illustrated by Leishmania infection in mice and leprosy in humans.
Mechanisms of Immune Evasion by
• Inhibition of phagolysosome formation
(Mycobacterium tuberculosis, Legionella
• Inactivating reactive oxygen and nitrogen
intermediates Mycobacterium leprae
• Disruption of phagosome membrane, escape
into cytoplasm Listeria monocytogenes