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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.

Hypersensitivities

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

write short notes on ligaments,curves and moverment of vertebral column.
mutesi Reply
what is the Analysis
ROHIT Reply
what is Anatomy
ROHIT Reply
it's a organs and bouns reading
AJITH
Cutting Up
Nonie
Cutting Up
Nonie
to dissect
Nonie
what usually cause blood pressurae
Abdullateef Reply
too much salt in the diet
Abuusu
older age
Abuusu
Even family history of high blood pressure
Abuusu
yes
Yaqub
too much salt in the diet
Yaqub
stress is the leading factor
Richard
smoking and too much alcohol consumption
Annu
obesity can also cause hypertension
Yaqub
high temperature of the body high salt of the body
Drs
how does the temperature affect the blood pressure?
Chidiebere
sex
Onavwie
What sex.?
Arshad
Male
Vikas
i mearnt gender,there's increased blood pressure in male than female
Onavwie
guys, read the question, involuntary pumping of heart causes the blood pressure in the arteries, he has not asked about high or low BP.
Jess
explain the cellular mechanism that produces tetanus and summation
Jenica Reply
epithelial cells polerity
jitendra Reply
tissues
Deepak
demonstrate the fluid replacement in the body
John Reply
the red blood cells is in the long bones or flat bones?
isbii
as age increases, the bone elongates .. will the joint vanish?
Sushruth Reply
what is anatomy?
Ivy Reply
structure
Allonda
discuss the organization of the body
Mwila Reply
explain the cellular mechanism that produces tetanus and summation
Chayanne Reply
explain why the muscle doesn't respond to low stimulus voltages
Chayanne
how would muscle contractions be affected if skeletal muscle fibers did have T - tubules?
Chayanne
tetanus is a disease caused by a bacteria causing rigidity and spasms of volutary muscles.. there is a prolonged construction of muscles caused by repeated stimuli
Marcus
muscles follow the "all or none law" when it comes to reponse to stimuli... muscle construction would have been affected because the T tubules are the conducting tracts that transport the or move the action potential in deporalizing the other parts of cell hence the muscle wont act as a single cell
Marcus
Skeletal muscle fibers do have t tubules that's how action potential propagates to spread throughout the muscle. Tetanus production is a phenomenon which is better explained in time rather then cellularly. Action potentials either separated in time or space are summated on the muscle and
Vikas
When the stimulus frequency hits more than 25 the individual twitches from the fibers summate and the muscle as a whole contracts. Cellulary, a good amount of calcium needs to be accumulated as is done by twitches adding together.
Vikas
what is the names of tarsus?
Fathia Reply
the region of the foot containing the seven tarsal bones.
Manja
the tarsal bones
Marcus
how the valves keep the blood moving in one direction?
Nonie Reply
They open and close during blood circulation,
Denis
Then valve open labb sound and valve close dabb sound
HARDIK
The valves for example the semilunar valves act to prevent back flow of blood from arteries to ventricles during ventricular diastole and help to maintain pressure on the major arteries .The aortic semilunar valve separate the left ventricle from opening of the aorta.
Denis
thank you
Nonie
😷
HARDIK
hi
Shakir
hello
Manja
Yes
kannan
what are estrogen and progesterone ? and their functions
Emmanuel
it's a body hormones and this is spread by women and it's can help to reproduction system...
HARDIK
yhe I also wana know
Lemasyanji
can we introduce ourselves and share contact?
Emmanuel
🤔
HARDIK
thanks
Emmanuel
i want ti study medicine.. what are the main course?
Emmanuel
Progesterone helps to maintain the endometrium wall which is later shed out of the body during the menstrual cycle
Smisha
Estrogen is another ovarian hormone which helps the primary follicle to develop into graafian follicle and cause ovulation
Smisha
what is decstro cardiac
priyanshi
Right sided heart in a guy
Vikas
Dextrocardia is a condition where the. heart lies in the right side of the thorax instead of the left and it occurs when the heart loops to the left instead of the right.
Idoko
hii
Vikas
can any talk me a scope of anatomy and physiology
Vikas
please
Vikas
It has valves that OPEN and close during circulation
xiao
What does the Thyroid gland means
Solomon Reply
It's a gland in your neck produces thyroid hormone maintains body metabolism
Vikas
how many joints are in the human foot?
Roghayeh Reply
I believe that is 33 joints
Ana
26 bones and 33 joints.
Amin
thank u.
Roghayeh
thanks
antouman

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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