IMMUNE SYSTEM 6.3 Defense against infectious disease

Define pathogen. Explain why antibiotics are effective against bacteria but not against viruses. Outline the role of skin and mucous membranes in defense against pathogens. Outline how phagocytic leucocytes ingest pathogens in the blood and in body tissues. Distinguish between antigens and antibodies. Explain antibody production Outline the effects of HIV on the immune system. Discuss the cause, transmission and social implications of AIDS

Pathogens and Infectious Infectious disease (communicable disease) is caused when another organism or virus invades the body (host) and lives there parasitically. Pathogen: is an organism or a virus that causes disease. Usually they are microorganisms. Vector: an organism that transmits a disease causing organism, or a device for transferring genes during genetic engineering. What are the non-communicable diseases?

PATHOGENS 1- Bacteria 2- Fungi 3-Viruses 4-Protozoa 5-Some invertebrate animals (flatworms, roundworm ……….)

IMMUNE SYSTEM ORGANS Spleen: The organ of the immune system that is located in the abdomen cavity. Degradation of old RBCs Storage of blood as a reserve in the event of any shortage Production of lymphocytes Production of fetal blood until birth Can we survive without our spleen????

Lymph nodes: Lymph nodes filter the lymphatic fluid and store special cells that can trap cancer cells or bacteria that are traveling through the body in the lymph fluid

Tonsils: The tonsils trap bacteria and viruses entering through the throat and produce antibodies to help fight infections.

Thymus Gland: The site of T lymphocyte cell differentiation. The thymus increases gradually in size and activity until puberty, becoming vestigial (useless) thereafter.

What is immunity? It is the recognition and removal of molecules, cells that foreign to the body. Immunity can be gained by two ways.

There are two types of immunity; 1)Non-specific immunity (innate immunity) 2)Specific immunity (acquired immunity)

1- Non-specific immunity The basic resistance to disease that a species possesses - the first line of defense against infection. Skin barrier HCl in the stomach Lysozyme enzyme in sweat/saliva ( to digest bacteria) Mucous membranes protecting mouth, anus, genitals. Phagocytic leucocytes.

SKIN It is the first line of defense. External skin is covered by dry dead cells with keratinized proteins. Folds or moist parts of the skin are good habitat for pathogens.

Mucus Inner lining of the body (respiratory tract and digestive tract) are covered by mucosa layer that secrete mucus for protection.

Phagocytic WBS Granulocytes, Monocytes

Interferons  protein that is produced by body cells to fight with viruses. Sythesized proteins inhibit the synthesis of some enzymes that are required for virus replication. Inflammation  The local response to injury, involving small blood vessels, the cells circulating within these vessels, and nearby connective tissue. Fever occurs.

White blood cells are fighting with bacteria.

2) Specific Immunity (acquired-adaptive immunity) It is provided by lypmhocytes which are specific to the bacteria. a) B lymphocytes: synthesize antibodies. Antibodies destroy bacteria (antigen). …. b)T lymphocytes: they kill the infected body cells to prevent spread the infectious.

How do the cells work? (Active or Passive immunity) Active immunity Gained by either direct contact with pathogen or get vaccine shot. Our body produce special antibodies against that pathogen. Passive immunity Gained by taking antibodies from another organisms (mother, serum from other animals). Our body does not produce antibody, instead it uses antibodies that come from other organisms. It is short term immunity. Ex. Serum which is used in snakebite

ANTIBODIES ARE BIOLOGICAL WEAPONS. HOW DO THEY KILL THE PATHOGEN?

ANTIBODIES Y-shaped proteins Produced by B cells Antibody recognizes the pathogen/antigen and binds to it (tagging it) This causes one of two things to happen: 1) Macrophages (killer cells) to come and ‘eat’ the bacteria (phagocytosis) Or 2) Other antibodies come and help out and kill the bacteria directly (cell lysis)

ANTIBIOTICS or ANTIBACTERIAL Antibiotics are used to treat infections caused by bacteria. (ex. Penicillin) A substance that kills or slows down the growth of bacteria. There is concern worldwide that antibiotics are being overused. Antibiotic overuse is one of the factors that contributes towards antibiotic resistance as the growing number of bacterial infections which are becoming resistant to antibacterial medications.

How do antibiotics kill bacteria? Remember bacterial life cycle! Antibiotics stop bacterial reproduction by blocking: 1- DNA polymerase 2- RNA polymerase 2- Enzyme for cell wall synthesis Are antibiotics effective against viruses? Think about viral life cycle!!

VIRUSES Viruses are known as ‘genes in a box’. They are made of protein coat (capsid) and and a nucleic acid either DNA or RNA but not both of them. They do not have metabolic reactions and can not reproduce themselves. They need a host cell to reproduce.

Viruses have two types of reproductive cycles. 1. In the lytic cycle, – viral particles are produced using host cell components, – the host cell lyses, and – viruses are released. 2. In the Lysogenic cycle – Viral DNA is inserted into the host – Viral DNA is duplicated along with the host chromosome during each host cell division. – The inserted phage DNA is called a prophage. – Most prophage genes are inactive. – Environmental signals can cause a switch to the lytic cycle, causing the viral DNA to be excised from the bacterial chromosome and leading to the death of the host cell. © 2012 Pearson Education, Inc.

Figure 10.17_s2 Phage Attaches to cell Phage DNA Bacterial chromosome The phage injects its DNA Lytic cycle The phage DNA circularizes 1 2 The cell lyses, releasing phages 4 New phage DNA and proteins are synthesized Phages assemble 3 OR Environmental stress Lysogenic cycle Many cell divisions The lysogenic bacterium replicates normally Prophage Phage DNA inserts into the bacterial chromosome by recombination 5 7 6

The cell lyses, releasing phages Figure 10.17_1 Phage Attaches to cell Phage DNA The phage injects its DNA Lytic cycle The phage DNA circularizes 1 New phage DNA and proteins are synthesized Phages assemble Bacterial chromosome

Figure 10.17_2 Phage Attaches to cell Phage DNA Bacterial chromosome The phage injects its DNA The phage DNA circularizes Environmental stress Many cell divisions The lysogenic bacterium replicates normally, copying the prophage at each cell division Prophage Phage DNA inserts into the bacterial chromosome by recombination Lysogenic cycle

Figure 10.20A Envelope Glycoprotein Protein coat RNA (two identical strands) Reverse transcriptase (two copies) HIV VIRUS (human immunodeficiency virus)

The AIDS virus makes DNA on an RNA template  AIDS (acquired immunodeficiency syndrome) is caused by HIV (human immunodeficiency virus).  HIV is an RNA virus, has two copies of its RNA genome, carries molecules of reverse transcriptase, which causes reverse transcription, producing DNA from an RNA template. © 2012 Pearson Education, Inc.

 After HIV RNA is uncoated in the cytoplasm of the host cell, 1.reverse transcriptase makes one DNA strand from RNA, 2.reverse transcriptase adds a complementary DNA strand, 3.double-stranded viral DNA enters the nucleus and integrates into the chromosome, becoming a provirus, 4.the provirus DNA is used to produce mRNA, 5.the viral mRNA is translated to produce viral proteins, and 6.new viral particles are assembled, leave the host cell, and can then infect other cells. The AIDS virus makes DNA on an RNA template © 2012 Pearson Education, Inc.

Figure 10.20B Viral RNA DNA strand Reverse transcriptase Double- stranded DNA Viral RNA and proteins CYTOPLASM NUCLEUS Chromosomal DNA Provirus DNA RNA

Effect of HIV on the immune system: AIDS HIV host cells are antibody secreting lymphocytes. HIV takes control of lymphocytes, and their number decreases. So, patient becomes vulnerable to attack by opportunistic infectious (pneumonia, meningitis, cancers that would normally be resisted by a person with a healthy immune system.

Treatment and prevention of AIDS Until there is a vaccine or a cure, the best way to stop AIDS is to educate people about how the virus is transmitted. HIV mutates very quickly. New strains are resistant to AIDS drugs. Drug-resistant strains now infect new patients.

The Social Consequence of AIDS Psychological Economic Child development and education Child health. Medical services provision National factors