The document summarizes resistance and immune responses to infectious diseases. It discusses the four main types of pathogens (viruses, bacteria, protozoa, helminths) and provides details on immune responses to specific pathogens like influenza virus, diphtheria bacteria, malaria protozoa (Plasmodium), and parasitic worms. It also notes that microbes have evolved ways to evade the immune system, such as antigenic variation, hiding in protected niches, and suppressing immune responses.

2. RESISTANCE AND
IMMUNE RESPONSES TO
INFECTIOUS DISEASES

3. GROUP MEMBERS
 ZAIB-UN-NISA
 SADAF RASHEED
 SOBIAAMEER
 ATIKA SHAKEEL
 MUTABASSIM ALI

4. INTRODUCTION
Despite innate and adaptive immune responses to
pathogens, infectious diseases which have plagued
human populations throughout history still cause
millions of deaths per year.
There are 4 main types of pathogens that cause
infectious diseases:
 Viruses
 Bacteria
 Protozoa
 Helminths

5. VIRAL INFECTION
The immune response to viral infections involve both:
 Humoral immunity
 Cell-mediated components
Antibody to a viral receptor can block viral infections of host cells. However, a number of viruses,
including influenza, are able to mutate their receptor molecules and thus evade the humoral
antibody response.
Once a viral infection has been established, cell-mediated immumity appears to be more important
than humoral.CD8 Tc and CD4 TH cells are the main components of cell-mediated antiviral defense.

6. INDUCTION OF ANTIVIRAL ACTIVITY
 Induction of antiviral activity by IFN-α and IFN-β.
 These interferons bind to the IFN receptor, which in turn induces the synthesis of both 2-
5(A) synthetase and protein kinase (PKR).
 The action of 2-5(A) synthetase result in the activation of RNAse L, which can degrade
messanger RNA.
 PKR inactivates the translation inititation factor elF-2 by phosphorylating it.
 Both pathways thus result in the inhibition of protein synthesis and thereby effectively
block viral replication.

7. INDUCTION OF ANTIVIRAL ACTIVIY

8. INFLUENZA VIRUS
 The influenza virus infects the upper respiratory tract and major
central airways in humans, horses, birds etc.
 The envelope is covered with neuraminidase and hemagglutinin
spikes, which are responsible for the attachment of the virus to the
host cells.
 Inside is an inner layer of matrix proteins surrounding the
nucleocapsid, which consist of eight ssRNA molecules associated
with nucleoprotein.
 The eight RNA strands encode ten proteins: PB1, PB2, PA, HA
(hemagglutinin), NP (nucleoprotein), NA (neuraminidase), M1,
M2, NS1 and NS2.

9. HOST RESPONSE TO INFLUENZA
ACTION
Two mechanism generate variations in influenza
surface antigens.
 In antigenic drift, the accumulation of point
mutations eventually yield a variant protein that is
no longer recognized by antibody to the original
antigen.
 Antigenic shift may occur by reassortment of an
entire ssRNA between human and animal virions
infecting the same cell. Only four of the eight RNA
strand are depicted.

10. BACTERIAL INFECTIONS
Bacteria enter the body either through a number of natural routes (e.g., the respiratory tract, the
gastrointestinal tract etc.) or through normally inaccessible routes opened up by breaks in mucous
membranes or skin.
There are four primarily steps in bacterial infection:
 Attachment to host cells
 Proliferation
 Invasion of host tissue
 Toxin-induced damage to host cells

11. IMMUNE RESPONSES TO BACTERIA

12. IMMUNE RESPONSE TO BACTERIA
 The immune response to extracellular bacterial infections is generally mediated by
antibody.
 Antibody can induce localized production of immune effector molecules of the
complement system.
 Antibody can also activate complement-mediated lysis of the bacterium, neutralize toxins,
and serve as an opsonin to increase phagocytosis.
 Some bacteria secrete protease enzymes that cleave IgA dimers, thus reducing the
effectiveness of IgA in the mucous secretions.
 Host defense against intracellular bacteria depends largely on CD4 T-cell-mediated
responses.

13. BACTERIAL DISEASES
DIPTHERIA

14. PROTOZOAN DISEASES
 Protozoans are unicellular eukaryotic organisms.
 They are responsible for several serious diseases in humans, including ambeoblasts,
African sleeping sickness, malaria and toxoplasmois.
 The type of immune response that develops to protozoan infection depend in part on the
location of the parasite within the host.
 Any protozoans have life cycle stages in which they are free in the bloodstream, during
these stages the humoral antibody is most effective..
 Many of these same pathogens are also capable of intracellular growth; during these
stages, cell-mediated immune reactions are effective in host defense.

15. LIFE CYCLE OF PLASMODIUM
 Sporozoites enter the Bloodstream when an infected mosquito takes a blood
meal.
 The Sporozoites migrate to the liver, where they multiply, transforming
liver hepatocytes into giant multinucleate schizonts, which release thousands
of merozoites into the bloodstream.
 The merozoites infect red blood cells, which eventually rupture, releasing
more merozoites.
 Eventually some of the merozoites differentiate into male and female
gametocytes, which are ingested by a mosquito and differentiate into
gametes.
 The gametes fuse to form a zygote that differentiates to the sporozoite stage
within the salivary gland of the mosquito.

16. IMMUNE RESPONSES TO PROTOZOANS
 Both humoral and cell-mediated immune responses have been implicated in immunity to
protozoan infections.
 Humoral antibody is effective against blood-borne stages of the protozoan life cycle.
 Once protozoans have infected host cells, cell-mediated immunity is necessary.
 Protozoans escape the immune response through several mechanisms.
 Trypanosoma brucei are covered by a glycoprotein coat that is constantly changed by a
genetic switch mechanism.
 Plasmodium, the causative agent of malaria, slough off their glycoprotein coat after
antibody has bound to it.

17. PROTOZOAN TRYPANOSOMA
(African sleeping sickness)

18. DISEASE CAUSED BY PARASITIC
WORMS (HELMINTHS)
 Helminths are large, multicellular organisms that reside in humans but do not ordinarily
multiply there and are not intracellular pathogens.
 Although helminths are more accessible to the immune system than protozoans.
 The immune system is not strongly engaged and the level of immunity generated to
helminths is often very poor.
 Several helminthes are important pathogens of domestic animals and invade humans who
ingest contaminated food.
 Taenia, a tapeworm of cattle
 Trichinella, the roundworm of pigs

19. IMMUNE RESPONSE TO HELMINTHS
 The response includes an IgE
humoral component and a
cell-mediated component
involving CD4 T cells.
 C = complement
 ECF = eosinophil
chemotactic factor
 PAF = platelet-activating
factor

20. RESISTANCE / IMMUNE EVASION BY
MICROBES
 Microorganisms have developed many means to resist or evade the immune system:
 Antigenic variation
 Growth in niches that are inaccessible to the host immune system
 Resistance to innate immune defense
 Impairment of effective T-cell antimicrobial responses by specific or nonspecific
immunosuppression.