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After seroconversion, the amount of virus circulating in the blood drops and stays at a low level for several years. During this time, the levels of CD4 + cells, especially helper T cells, decline steadily, until at some point, the immune response is so weak that opportunistic disease and eventually death result. CD4 is the receptor that HIV uses to get inside T cells and reproduce. Given that CD4 + helper T cells play an important role in other in T cell immune responses and antibody responses, it should be no surprise that both types of immune responses are eventually seriously compromised.

Treatment for the disease consists of drugs that target virally encoded proteins that are necessary for viral replication but are absent from normal human cells. By targeting the virus itself and sparing the cells, this approach has been successful in significantly prolonging the lives of HIV-positive individuals. On the other hand, an HIV vaccine has been 30 years in development and is still years away. Because the virus mutates rapidly to evade the immune system, scientists have been looking for parts of the virus that do not change and thus would be good targets for a vaccine candidate.


The word “hypersensitivity” simply means sensitive beyond normal levels of activation. Allergies and inflammatory responses to nonpathogenic environmental substances have been observed since the dawn of history. Hypersensitivity is a medical term describing symptoms that are now known to be caused by unrelated mechanisms of immunity. Still, it is useful for this discussion to use the four types of hypersensitivities as a guide to understand these mechanisms ( [link] ).

Immune hypersensitivity

This table describes different types of hypersensitivity. In Type I (IgE-Mediated Hypersensitivity), IgE is bound to mast cells via its Fc portion. When an allergen binds to these antibodies, crosslinking of IgE induces degranulation. Type I causes localized and systemic anaphylaxis, seasonal allergies including hay fever, food allergies such as those to shellfish and peanuts, hives, and eczema. In Type II (IgG-Mediated Hypersensitivity), cells are destroyed by bound antibody, either by activation of complement or by a cytotoxic T cell with an Fc receptor for the antibody (ADCC). Examples are when red blood cells are destroyed by complement and antibody during a transfusion of mismatched blood types or during erythroblastosis fetalis. In Type III (Immune Complex-Mediated Hypersensitivity), antigen-antibody complexes are deposited in tissues, causing activation of complement, which attracts neutrophils to the site. Most common forms of immune complex disease are seen in glomerulonephritis, rheumatoid arthritis, and systemic lupus erythematosus. In Type IV (Cell-Mediated Hypersensitivity), Th1 cells secrete cytokines, which activate macrophages and cytotoxic T cells and can cause macrophage accumulation at the site. Most common forms are contact dermatitis, tuberculin reaction, and autoimmune diseases such as diabetes mellitus type I, multiple sclerosis, and rheumatoid arthritis.
Components of the immune system cause four types of hypersensitivity. Notice that types I–III are B cell mediated, whereas type IV hypersensitivity is exclusively a T cell phenomenon.

Immediate (type i) hypersensitivity

Antigens that cause allergic responses are often referred to as allergens. The specificity of the immediate hypersensitivity    response is predicated on the binding of allergen-specific IgE to the mast cell surface. The process of producing allergen-specific IgE is called sensitization, and is a necessary prerequisite for the symptoms of immediate hypersensitivity to occur. Allergies and allergic asthma are mediated by mast cell degranulation that is caused by the crosslinking of the antigen-specific IgE molecules on the mast cell surface. The mediators released have various vasoactive effects already discussed, but the major symptoms of inhaled allergens are the nasal edema and runny nose caused by the increased vascular permeability and increased blood flow of nasal blood vessels. As these mediators are released with mast cell degranulation, type I hypersensitivity    reactions are usually rapid and occur within just a few minutes, hence the term immediate hypersensitivity.

Most allergens are in themselves nonpathogenic and therefore innocuous. Some individuals develop mild allergies, which are usually treated with antihistamines. Others develop severe allergies that may cause anaphylactic shock, which can potentially be fatal within 20 to 30 minutes if untreated. This drop in blood pressure (shock) with accompanying contractions of bronchial smooth muscle is caused by systemic mast cell degranulation when an allergen is eaten (for example, shellfish and peanuts), injected (by a bee sting or being administered penicillin), or inhaled (asthma). Because epinephrine raises blood pressure and relaxes bronchial smooth muscle, it is routinely used to counteract the effects of anaphylaxis and can be lifesaving. Patients with known severe allergies are encouraged to keep automatic epinephrine injectors with them at all times, especially when away from easy access to hospitals.

Questions & Answers

Card 5 / 12: For whom would an appreciation of the structural characteristics of the human heart come more easily: an alien who lands on Earth, abducts a human, and dissects his heart, or an anatomy and physiology student performing a dissection of the heart on her very first day of class? Why?
Gelowe Reply
what are regular shaped cells with granules in the cytoplasam
Kabita Reply
I need sylubuss of clinical officers book
Omary Reply
cholesterol normal value is
less than 200mg/dl
100 to159mg/dL
Early this wk. I had some "A & P" questions & answers unfortunately didn't save them, Is there any way I can have them back ,so as 2 save them?. Thnx.
what are the functions of the female reproductive system
Lister Reply
it produces the female egg necessary for reproduction, called the Ova or Oocytes. The system is designed to transport the Ova to the site of fertilization.
Female reproductive system was mainly functioned to produce ova(ovum) (female eggs) Into which will be fertilized by male gamete to produce zygote
absolutely right
wa qalad nimco rage iska hubi
waxwalba ka fikirbay ubaahantahay
ha wayo jawabtoda wa qabyo nimco wey ku raacdat
ha wayo jawabtoda wa qabyo nimco wey ku raacday
wxayaabaha qaarkood waaa in aan u feejignaano
asc if I try female reproductive system has two function the first is to produce egg cell and the second is to protact and nourish the offspring until birth
what is stercobilinogen
Hancerich Reply
fecal urobilinogen. Created by bacteria in the gut. a chemical that gives feces brown color.
next question pls.
The rate of diffusion increases if the
What's the answer?
it's a breaking down of haemoglobin and it's a chemical made by bacteria
Thnx Dev Raj.
yup so any more
yes I sure do need more "Questions" & "Answers". I'm learning whole lot. Thnx.
what is the greatest muscle of the body
Lungu Reply
gluteus maximus
pls!!! more "A&P" questions & answers. Thnx.
Gluteus maximus
Describe anatomy of cardiovascular system?
cardiovascular system is a group of organs coming together to perform the circulation of blood. The organs invoked are the heart and the blood vessels with blood being the tissue. The heart is a pump and it pumps oxygenated blood through the systemic circuit and deoxygenated blood through the pulmon
pulmonary circuit.
more A&P questions pls. Thnx.
If an ANOVA yields a significant F value, you could rely on ________ to test significant differences between group means.
Dane Reply
what's ANOVA
analysis of variance
plz what you mean with "ANOVA" first
anova means analysis of variance, a statistical method in which the variation in a set of observations is divided into distinct components.
M value ot test
What does it mean by M value ot test?
formation of red blood cells
Biketi Reply
explain why... lower back pain in ovarian cancer
Srijoni Reply
we says that protoplasm is the living part of us How?
Muzamil Reply
is the leaving part of our cellular structure.
it is the leaving part of our blood cellular structure also
what is receptor?
Preity Reply
an organ or cell able to respond to light, heat, or other external stimulus and transmit a signal to a sensory nerve.
Has anyone taken the first exam?
hey what is the process after your food is swallowed? how long does it take to get to the stomache until it is released as waste?
Fednise Reply
that is such a broad question. as you begin to swallow its various doses down the alimentary canal that brings the food into your stomach.then depending on whether it's a protein carbohydrate fat that dictates what function takes place in your stomach. these are all steps of digestion.
typo sorry it's peristalsis , wave-like projections that push food down your alimentary canal etc. digestion starts in your mouth ends in your large intestines (colon anus)
some of the many processes of digestion include hydrolysis dehydration synthesis denaturation of proteins etc. you have to be more specific.
there's many different contributing factors the how long it takes food to convert into waste. remember fats, triglycerides proteins and carbohydrates all breakdown two different monomers and structures. you should be looking up metabolic processes.
depending how much fiber you have in your diet dictates how much water is brought to your intestines that has to do with excretion whether fiber is insoluble or soluble. this is an anatomy and physiology app. to simply say the stomach will empty its contents in 2 to 3 hours would do you a disservice
can the study of anatomy relate to medical technologies
Lean Reply
how can I understand micro biology and anatomy better.
someone to help me understand glycogeneogenesis
what are the major branches of the aorta?
look youtube video

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