INTRODUCTION TO IMMUNOLOGY.pdf

8/11/2019 INTRODUCTION TO IMMUNOLOGY.pdf

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INTRODUCTION TIMMUNOLOGY


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General Properties ofImmune Responses

Innate and Adaptive Immunity 4Types of Adaptive Immune Responses 5

Cardinal Features of Adaptive Immune

PhasesRec

Acti


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4 Section I INTRODUCTION TO IMMUNOLOGY

Table 11 Effectiveness of Vaccination for Some Common Infectious Diseas

Disease

MaximumNumber

of Cases

Year of Max

Number of C

Diphtheria 206,939 1921

Measles 894,134 1941

Mumps 152,209 1968

Pertussis 265,269 1934

Polio (paralytic) 21,269 1952

Rubella 57,686 1969

Tetanus 1,560 1923

Haemophilus influenzaetype B infection 20,000 1984

Hepatitis B 26,611 1985

This table illustrates the striking decrease in the incidence of selected infectious disease

In some cases, such as with hepatitis B, a vaccine has become available recently, an

decrease.

Adapted from Orenstein WA, AR Hinman, KJ Bart, and SC Hadler. Immunization.InGL Ma


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Table 12 Features of Innate and Adaptive Immunity

Innate Ad

Characteristics

Specificity For structures shared by groups of

related microbes

Fo

Diversity Limited Ve

Memory None Ye

Nonreactivity to self Yes Ye

Components

Physical and chemical barriers Skin, mucosal epithelia; antimicrobial

chemicals

Lym

Blood proteins Complement An

Cells Phagocytes (macrophages, neutro-

phils), natural killer cells

Lym


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BOX 11 Evolutionof the Immune System

Mechanisms for defending the host against foreign invaders are

present in some form in all multicellular organisms. These mecha-nisms constitute innate immunity. The more specific and specialized

defense mechanisms that constitute adaptive immunity are found in

vertebrates only.

Various cells in invertebrates respond to microbes by enclosing

these infectious agents within aggregates and destroying them.

These responding cells resemble phagocytes and have been called

phagocytic amebocytes in acelomates, hemocytes in molluscs and

arthropods, coelomocytes in annelids, and blood leukocytes in tuni-

cates. Invertebrates do not contain antigen-specific lymphocytes and

do not produce immunoglobulin molecules or complement proteins.

However, they contain a number of soluble molecules that bind toand lyse microbes. These molecules include lectinlike proteins, which

bind to carbohydrates on microbial cell walls and agglutinate the

microbes, and numerous lytic and antimicrobial factors such as lyso-

zyme which is also produced by neutrophils in higher organisms

tion in vertebr

either is not less, such resu

surface molecu

cules may be t

brates.

The variou

pear to have a

increasingly sp

nal features of

nonself discrim

in the lowest

creases progrecontain antibod

with the develo

ing a diverse re

immunoglobulin


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w a s o r ig ina l ly d efi ne d a s the ty pe o f im m uni ty tha tco uld b e tr a nsf er re d to uni m m uniz ed , o r na i v e, individuals by ant ibody-conta ining cell-free portionsof the blood (i.e., plasma or serum [once called hu-mors]) obtained from previously immunized indi-viduals. Similarly, cell-mediated immunity w as de-fi n ed a s th e form of im mun ity th at ca n betransferred to naive individuals w ith cells (T lym-phocytes) from immunized individuals but not w ithplasma or serum.

Clinically, we do not measure immunity by test-ing an individuals resistance to an infection. Immu-nity is actually assayed by determining whether in-d iv id ua ls w ho ha v e b ee n pre vio usl y e xpose d to af o re ig n sub sta nce m a ni fe st a d etec ta b le r ea c tio nw he n r ee x po se d to , o r cha l le nge d w ith, tha t sub -stance. Such a reaction is an indication of sensitiv-ity to cha l le nge a nd ind iv id ua ls w ho ha v e b ee n

phagocytesprove that mediated bb eca m e fi rGeorge Matracellular adoptively We now kimmunity ition in conto eliminate


CARDINAL F

RESPONSES

All humoraf or eign a nproperties


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w ays toci enc y Thus, hmunity or by thfection type of tha t claimmunT lymphone clasthe m esuch spbook.

Self-l imw a ne wreturnin


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host to custom design responses to best combatman y different types of microbes. Self-limitation al-l o w s the s y s te m to r e tur n to a s ta te o f r e s t a f te r i teliminates each foreign antigen and to be preparedto respond to other antigens. Self-tolerance and theability to distinguish betw een self and nonself arevital for preventing reactions a gainst ones ow n cellsand tissues w hile maintaining a diverse repertoire oflymphocytes specifi c for foreign antigens.

CELLULAR COMPONENTS OF THE ADAPTIVEIMMUNE SYSTEM

The pr in cipal cel ls of the immu ne system are lym-ph ocyt es, accessor y cell s, an d eff ector cell s. Lympho-cytes are th e cells that specifically recognize and re-spo nd to f o re ig n a ntig ens a nd a r e, the re fo r e, themediators of humoral and cellular immunity There

helper T cells. T ceTheir a ntigtinct from C ha pte r 6(CTLs) ha vr eco g niz e pro teins thhistocompapressed onthese T ceassociated In responssecrete proto stimulatthe T cellsmacrophagthat produ



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volved in innate immunity against viruses and otherintracellular microbes. We will return to a more de-tailed discussion of the properties of lymphocytes inChapter 2.

The initiation and development of adaptive im-mune responses depend on nonlymphoid cells calledaccessory cells, wh ich are not specific for differentantigens but play important roles in antigen displayto and activation of antigen-specifi c lymphocytes.Mononuclear phagocytes, dendritic cells, and severalother cell populations fun ction as accessory cells inthe induction of immune responses. The activationof lymphocytes by antigen leads to the generation ofnum e ro us m e cha ni sm s tha t f unctio n to e lim ina tethe antigen. The effector phase of antigen elimina-tion often requires the participation of cells calledeffector cells. Activated T lymphocytes, mononu-clear phagocytes and other leukocytes function as

migrate toeliminate t

PHASES OFA dapti v e thr ee phasti on of lym6). All imcifi c recogto the actthe a ntig eeffector mfunction othe antigemune respIn the folt a n t f ea t u


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Activationof Lymphocytes

The activation of lymphocytes r equir es tw o dist in ct signals, the first bein g an tigen and the second bein gei th er microbial products or components of in nateimmune responses to microbes (Fig. 1 8). This ideais called t he two-signal hypothesis for lymphocyteactivation. The requirement for antigen (so-calledsignal 1) ensures that the ensuing immune responseis specific. The requirement for additional stimulitriggered by microbes or innate immune reactions( sig na l 2 ) e nsur es tha t i m mune r esponse s a r e i n-duced when they are needed (i .e . , against microbesa n d o t h er n o x io u s su bst a n ce s) a n d n o t a ga in st

harmless substances, including self antigens. We willreturn to the nature of second signals for lympho-cyte activation w hen w e discuss this process in moredetail (see Chapters 8 and 9) and in the context ofinnate immunity (see Chapter 12)

The resond signacel lular prtor and me

SYNTHESIS

Early aftescribe genthesize a vclude secrthe g ro w tthemselveceptors, w

to cytokingene trans

CELLULAR P


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Selected Readings

Burnet FM. A modification of Jernes theory of antibodyproduction using the concept of clonal selection. Aus-tralian Journal of Science 20:6769, 1957.

du Pasquier L, and M Flajnik. Origin and evolution of thevertebrate immune system. In WE Paul (ed). Funda-

mental Imers, Phila

Jerne NK. Ttion. Proc

USA 41:8Silverstein A

San Diego


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INTRODUCTION TO IMMUNOLOGY.pdf