Sistem Imun

Sistem Imun

Pengertian :Tersusun dari sel-sel dan jaringan yang membentuk imunitas, yaitu kekebalan tubuh terhadap infeksi atau penyakit.

Fungsi :• Penangkal “benda asing” yang masuk ke dalam tubuh;• Menyingkirkan sel dan jaringan yang sudah tua dan mati;• Sebagai pendeteksi adanya sel-sel abnormal, termutasi,

atau ganas, serta menghancurkannya

A.Macam-Macam Sistem Pertahanan Tubuh

1. INNATE IMMUNITY (Pertahanan Tubuh non Spesifik)• Pertahanan pertama yang dimiliki oleh tubuh. • Memiliki respon non-spesifik terhadap patogen.• Merespon patogen atau antigen secara cepat.• Memperlakukan semua jenis patogen atau antigen secara

sama.

INNATE IMMUNITY Rapid responses to a

broad range of microbes

ACQUIRED IMMUNITYSlower responses to specific microbes

External defensesInternal defensesSkin

Mucous membranesSecretions

Phagocytic cellsAntimicrobial proteinsInflammatory responseNatural killer cells

Humoral response(antibodies)

Cell-mediated response(cytotoxic lymphocytes)

Invadingmicrobes

(pathogens)

Figure 43.2

• Ada dua jenis pertahanan non-spesifik, eksternal dan internal.

a. EXTERNAL DEFENSES (Garis Pertahanan Pertama)Pertahanan pertama melawan antigen. Terdapat

beberapa jenis: Pertahanan fisik Pertahanan mekanik Pertahanan kimiawi Pertahanan biologis

1) Pertahan Fisik Pertahanan pertama terhadap antigen. Menghalangi masuknya mikroorganisame dan

virus. Termasuk dalam pertahanan fisik adalah

kulit dan membran mukosa.KULIT

• Penghalang fisik bagi patogen yang masuk ke dalam tubuh..

• Mengandung keratin dan sangat sedikit air.• Menghambat pertumbuhan mikroorganisme.• Selain pertahanan fisik, kulit juga

berperan sebagai pertahanan kimiawi dengancara: Mensekresikan minyak dari kelenjar minyak dan mensekresikan keringat dari kelenjar keringat

MEMBRAN MUKOSA• Pertahanan pertama dalam sistem respirasi

tubuh kita.• Ada yang dilengkapi dengan silia yang

berfungsi untuk menjerat patogen.• Dapat mensekrisakn mukus yang juga bisa

menjerat patogen.

2) Pertahanan Mekanik Rambut hidung, berfungsi sebagai filter

udara yang melewati saluran hidung. Silia pada membran mukus juga berfungsi

untuk menangkap antigen yang masuk.

3) Pertahanan Kimiawi Pertahanan dengan cara mensekresikan zat-

zat yang dapat menghambat dan mematikan pertumbuhan antigen.

Air mata, mukus, saliva, dan keringat merupakan contoh zat yang dapat menghambatpertumbuhan organisme.

Zat sekresi tersebut mengandung lisozim yang menjadi katalis dalam reaksi hidrolisis dinding bakteri.

Zat sekresi lain yang pentik adalah asam hidroklorik yang berfungsi membunuh mikroorganisme yang masuk ke lambung.

4) Pertahanan Biologis Di kulit dan membran mukosajuga terdapat

populasi bakteri tidak berbahaya yang menghambat pertumbuhan bakteri patogen dengan cara bersaing dengan bakteri patogen dalam memperoleh nutrisi.

b. INTERNAL DEFENSES (Garis Pertahanan Kedua) Bekerja apabila antigen dapat melewati garis

pertahanan pertama. Bekerja secara nonspesifik.

Figure 43.3

10m

1) LeucocyteSel darah putih memiliki beberapa jenis:1. Neutrophil à the function is for

phagocytosis (process of eating the bacteria).The characteristic :

o The nucleus has Lobeso The biggest Leucocyte.

2. Eosinophil à play role in allergic reaction.3. Basophile à play role in inflammation

(peradangan).o Basophile release chemical substance

like Histamine which cause inflammation reaction.

4. Monocyte à the function is for phagocytosis.o Big size cell with nucleus and the shape

like kidney.o Monocyte growth become Macrophage and

the function also as a phagocytosis.o White blood cells called macrophages

trap and engulf cell debris and pathogens.

o Once a white cell has left the blood vessel and migrated to the enemy, the next job is to EAT the microbe.

o The macrophage is a large phagocyte. A phagocyte is an eating cell (phago = "eating", cyte = "cell") which engulfs invaders.

5. Lymphocyte à play role in specific immunity respond.

o Lymphocytes - are a type of white blood cell capable of producing a specific immuneresponse to unique antigens. They produce antibodies which are chemicals that mark pathogens for destruction.

2) Phagocytosis It performed by neutrophil and monocyte

(kind of leucocyte).

Where the Leucocyte engulf the pathogen then bring it into vacuole in that cytoplasm. And then digested by lytic enzyme.

3) Inflammation Or swelling of tissues is the fast reaction

against broken tissue. It’s like response toward insect bite, hard

hit, wound, etc.The signs of inflammation are like:

• Appear red colour in skin. It caused enlarged of blood vessel , and blood flow increase to the broken tissue

• Heat arising in skin. It caused faster blood flow

• Swelling occur. Increasing of blood flow that caused so much tissue liquid enter tobroken tissue.

• Pain occur. The swollen tissue pushed the receptor and nerve.

• Inflammation is important because it avoidspread of infection and speed up the healing process.

2. ACQUIRED IMMUNITY (Pertahanan Spesifik)• Bekerja ketika ada antigen yang masuk.• Bekerja lebih lambat.• Melibatkan lymphocyte.Terdapat dua jenis immunitas: Antibody-mediated immunity, melibatkan aktivasi dan

seleksi klonal sel B, dan mengsekresikan antibodi. Cell-mediated immunity, melibatkan aktivasi dan seleksi

klonal cytotoxic T cell.

a. LYMPHOCYTE DEVELOPMENT Berasal dari stem cells (sel punca) yang berada

di sumsum tulang. Awalnya semua lymphocyte sama, tergantung proses

pematangannya dimana.

Figure 43.14

Humoral immune response Cell-mediated immune response

First exposure to antigen

Intact antigensAntigens engulfed and displayed by dendritic cellsAntigens displayedby infected cells

Activate Activate Activate

Gives rise to Gives rise to Gives rise to

B cell HelperT cell

CytotoxicT cell

Plasmacells

MemoryB cells

Active and memory helperT cells

Memory cytotoxicT cells

Active cytotoxicT cells

Secrete antibodies that defend againstpathogens and toxins in extracellular fluid

Defend against infected cells, cancer cells, and transplanted tissues

Secretedcytokinesactivate

b. B Cells Receptor for Antigen Mengikat secara spesifik terhadap antigen

tertentu. Sering disebut membran antibodi atau membran

immunoglobulin.

Figure 43.10

Bone marrow

Lymphoidstem cell

B cell

Blood, lymph, and lymphoid tissues(lymph nodes, spleen, and others)

T cell

Thymus

Figure 43.8a

Antigen-bindingsite

Antigen-binding site

Disulfidebridge

Lightchain

Heavy chains

Cytoplasm of B cell

VA B cell receptor consists of two identical heavy chains and two identical light chains linked by several disulfide bridges.

(a)

Variableregions

Constantregions

Transmembraneregion

Plasmamembrane

B cell

V

VC

C CC

V

T Cells Receptor for Antigen• Terdiri dari dua rantai polipeptida yang berbeda.• Berikatan dengan MHC molecules pada sel yang terinfeksi.

Antibody Amolecules

Antigen

Antibody Bmolecule

Antigenicdeterminants

Antigen-bindingsites

c. CLASS I MHC MOLECULES Ditemukan hampir di seluruh sel tubuh yang

terinfeksi. Berikatan dengan cytotoxic T cells.

d. CLASS II MHC MOLECULES Ditemukan di dendritic cells, makrofaga dan B sel. Berikatan dengan helper T cells.

B.ANTIBODY-MEDIATED IMMUNITY• Tidak melibatkan sel, hanya melibatkan senyawa kimia

yang disebut antibodi.• Menyerang antigen dan patogen sebelum mereka dapat

menyerang tubuh.

Microbe Antigen-presentingcell

Antigenfragment

Class II MHCmoleculeT cellreceptor

Helper T cell

A fragment offoreign protein(antigen) inside thecell associates withan MHC moleculeand is transportedto the cell surface.

1

The combination ofMHC molecule andantigen is recognizedby a T cell, alerting itto the infection.

2

(b)

Antigen molecules

Variety ofB cells in a lymph node

Cell growthdivision, anddifferentiation

Clone of manyeffector cellssecretingantibodies

Antibodymolecules

1. ANTIBODY CLASSES

21 3

B cell

Bacterium

Peptide antigen

Class II MHCmolecule

TCR

Helper T cell

CD4

Activated helper T cell Clone of memory

B cells

Cytokines

Clone of plasma cellsEndoplasmicreticulum of plasma cell

Macrophage

After a macrophage engulfs and degradesa bacterium, it displays a peptide antigencomplexed with a class II MHC molecule.A helper T cell that recognizes the displayed complex is activated with the aid of cytokines secreted from the macrophage, forming a clone of activated helper T cells (not shown).

1 A B cell that has taken up and degraded the same bacterium displays class II MHC–peptide antigen complexes. An activated helper T cellbearing receptors specific for the displayedantigen binds to the B cell. This interaction,with the aid of cytokines from the T cell,activates the B cell.

2 The activated B cell proliferatesand differentiates into memoryB cells and antibody-secreting plasma cells. The secreted antibodies are specific for the same bacterial antigen that initiated the response.

Figure 43.17

2. ANTIBODY-MEDIATED DISPOSAL OF ANTIGENS• Mekanisme penghancuran yang dibantu oleh antibodi yang

telah disekresikan oleh sel B.

Figure 43.18

First Ig class produced after initial exposure to antigen; then its concentration in the blood declines

Most abundant Ig class in blood; also present in tissue fluidsOnly Ig class that crosses placenta, thus conferring passive immunity on fetus

Promotes opsonization, neutralization, and agglutination of antigens; less effective in complement activation than IgM (see Figure 43.19)

Present in secretions such as tears, saliva, mucus, and breast milk

Triggers release from mast cells and basophils of histamine and other chemicals that cause allergic reactions (see Figure 43.20)

Present primarily on surface of naive B cells that havenot been exposed to antigens

IgM(pentamer)

IgG(monomer)

IgA(dimer)

IgE(monomer)

J chain

Secretorycomponent

J chain

Transmembraneregion

IgD(monomer)

Promotes neutralization and agglutination of antigens; very effective in complement activation (see Figure 43.19)

Provides localized defense of mucous membranes byagglutination and neutralization of antigens (seeFigure 43.19)

Presence in breast milk confers passive immunity onnursing infant

Acts as antigen receptor in antigen-stimulated proliferation and differentiation of B cells (clonal selection)

3. Cell-mediated Immunity• Response immune which involving cells that directly

attack strange organism.• Lymphocyte T involved there. When it activated will

kill some microorganism. But most of them attack body cells which infected.

• Body using that immune response mechanism for dealing with parasite multicellular, fungus, cancer cells, and also attack transplant organ which is considered as a strange cell.

• Lymphocyte T also react toward specific antigen. When apathogen infected body for first time, each antigen on the pathogen cell surface will stimulate one cell Lymphocyte T to split and make clone. Some of clone will be memory cells which stayed in body to prepare

Binding of antibodies to antigensinactivates antigens by

Viral neutralization(blocks binding to host)

and opsonization (increasesphagocytosis)

Agglutination ofantigen-bearing particles,

such as microbesPrecipitation ofsoluble antigens

Activation of complement systemand pore formation

Bacterium

Virus Bacteria

Solubleantigens Foreign cell

Complementproteins

Enhances

Phagocytosis

Leads to

Cell lysis

MacrophageFigure 43.19

secondary immune response if infection happen again by the same pathogen.

• Another clone will grow to be one of the 3 types of T cells

a. Helper T cell (TH cells) • This T cell help or controlled the component of

another specific immune response.b. Killer T cell

• Also called as cytotoxic T cell (TC cells, or CTLs). It attack infected body cell and pathogen cells which relatively large (ex/ parasite) directly. Both of them meet, membrane meet membrane, and killer T cell will punch their cell opponent. The infected cell or parasite cell will loose its cytoplasm and die.

c. Suppressor T cellHave function to decrease and stop immune response. That’s mechanism required when infection successfully resolved. This mechanism is important because if body continuously produce antibody and stimulate B and T cells to continue to divide in not required time, the immune system component could damage the body's own tissue.

Disease PreventionActive ImmunityOriginates from activated lymphocytes triggered by antigens onthe surface of pathogenic cells. If the process occurs during natural infection, its calles natural active immunity. It can also be triggered artificially by a process called vaccination.

Artificial active immunity: VaccinationVAKSIN

• Kekebalan tubuh juga dapat dilakukan dengan memasukkan penyakit tertentu yang telah melemah. Peristiwa ini disebut imunisasi buatan. Buatan imunisasi diperoleh melalui vaksin.

• Vaksin à cairan yang mengandung antigen (mikroorganisme atau racun) yang telah melemah. Metode Vaksinasi pertama kali diperkenalkan oleh Edward Jenner pada tahun 1976.

• Vaksinasi umumnya memiliki jangka waktu tertentu, sehingga vaksin harus diberikan lagi setelah beberapa saat. Hal ini menyebabkan jumlah zat anti dalam tubuh menurun seiring waktu, sehingga kekebalan tubuh juga menurun.

• Vaksin diberikan, selain membentuk antibodi, biasanya disertai dengan gejala demam ringan yang terjadi selama 1-2 hari dan juga rasa sakit atau bengkak di bagian tubuh yang disuntikkan.

Vaksin yang baik akan menghasilkan daya kebal yang cukup tinggi.Hal-hal yang dapat menyebabkan vaksin rusak:

• Panas yang dapat menghancurkan semua jenis vaksin • Sinar matahari terutama menghancurkan vaksin BCG dan

campak • Pembekuan dapat menghancurkan vaksin yang terbuat dari

toksoid seperti DPT dan TT • Desinfektan atau antiseptik (alkohol, sabun, spiritus)

dapat merusak vaksin. Antibacterial

• In this century, people have found some drugs for kill bacteria that caused diseases which known as antibacterial / antibiotic. Antibacterial is chemical compound that produced by microorganism, which can kills another microorganism.

• Contoh : Penisilin, tetrasiklin