Ocular Pathology_Inflammation1.ppt

7/29/2019 Ocular Pathology_Inflammation1.ppt

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OPHTHALMICPATHOLOGY


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Adaptive immunity is a host response set by a specificenvironmental antigen.

An antigen usually represents an alien substance completely

foreign to the organism, and the immune system must generate a

specific receptor against it that must recognize a unique molecular

structure in the antigen for which no specific preexisting receptor

was present.

The organism defends itself by the following steps:

Recognizing the unique foreign antigenic substance as

distinguished from self.

Processing the unique antigen with receptors newly created byspecialized tissues.

Generating unique antigen-specific immunologic effector cells (T

and B lymphocytes) and unique antigen-specific soluble effector

molecules (such as antibodies), which function to remove

antigenic substance from the organism


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The adaptive immune system is not genetically predetermined but

evolves as an ongoing way for an individual's T and B lymphocytes

to continually generate new antigen receptors through

recombination, rearrangement, and mutation of the germline genetic

structure.

This creates a vast repertoire of novel antigen receptor molecules

that vary tremendously among individuals within a given species.


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Innate immunity is a pattern recognition response to :

Identify various offensive stimuli in an antigen-independent manner

Respond in a stereotyped, preprogrammed fashion determined bythe preexistence of receptors for the stimulus.

Generate generic() biochemical mediators and

cytokines that recruit nonspecific effector cells, especiallymacrophages and neutrophils, to remove the offending stimulus in anonspecific manner(ie. phagocytosis or enzymatic degradation).

The stimuli of innate immunity interact with receptors that have beengenetically predetermined by evolution to recognize and respond to

molecular motifs on triggering stimuli. These motifs often include a specific amino acid sequence, certain

lipoproteins, certain phospholipids, or other specific molecularpatterns.


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The receptors of innate immunity are identical among all individuals

within a species. The innate immune response to acute infection is the classic

example of this process.


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Receptor activation Both responses use receptors present on white blood cells to

recognize offending stimuli, but the recognition receptors arefundamentally different.

Inflammatory or noninflammatory responses

Both responses can trigger inflammation, but they usually operateat a subclinical level so that the individual is unaware of theresponse.

Nonspecific effector cells and molecules Although only the adaptive immune response employs T and B

lymphocytes as antigen-specific effector cells, both forms of

immunity useneutrophils, eosinophils, and monocytes asnonspecific effector cells and the same chemical mediators asamplification systems.


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Triggering stimuli Adaptive immunity is triggered by an antigen, usually in the form of a

protein, although carbohydrates or lipids can sometimes be antigenic.Innate immunity is triggered by bacterial toxins and cell debris, oftenin the form ofcarbohydrate, phospholipid, and other nonproteinmolecules.

Recognition receptors

The antigen receptors of adaptive immunity, such as antibodymolecules and T-cell antigen receptor molecules, are specific for eachantigen, recognizing unique molecular regions of an antigen calledepitopes. The receptors used by innate immunity, such as scavengingreceptors or toxin receptors, recognize conserved molecular patternsor motifs shared among various triggering stimuli.

Time of onset after triggering Because adaptive immune responses are acquired, they require

recognition, processing, and effector phases that need several daysfor activation.

Innate immunity is preprogrammed, requiring only the directactivation of a cellular receptor to initiate an effector response within

hours.


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Memory

Adaptive immune responses demonstrate memory, so that on

second exposure to the same antigen, the release of effectors is

more vigorous and rapid than during the original response. Innate

responses are genetically preprogrammed to react stereotypically toeach encounter.

Specificity

Adaptive immune responses demonstrate specificity for each unique

offending antigen. Innate responses do not.

Ocular Pathology_Inflammation1.ppt

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