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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

what's primary active transport
hassan Reply
is simply the movement of substances across the cell with the use of ATP
John
what is oesophagus?
Bhavani Reply
oesophagus also known as food pip
ABDULLAH
What is the meaning of dissection
Beryl Reply
what's the meaning of polar?
Jackson Reply
Sign of anaemia or whitish color or Hgb luck
Kassahn
Are you talking of Polar anaemia or what, because the word polar doesnt have one meaning
Kingsley
what are the three types of adrenocorticoids hormones
Lubega Reply
glucocorticoids mineralocorticoid and catecholamines
Kartik
what is polar and non-polar
Jackson Reply
polar unequal share of electron while non polar is equal share
Quran
why are phosphate molecules negatively charged?
Jackson Reply
Bocz of unpaired elections
Javid
because of unpaired electrons
ABDULLAH
what are amphipathic molecules?
Jackson Reply
Amphipathic molecules are molecules with both polar and non polar regions
Mohammed
How does the male organ develop
MADUBULA Reply
Hw does the male organ develop
MADUBULA
Review your questions madam
Aliyu
what is anaphylaxis?
Rugut Reply
it is an imagency condition resulting from abnormal and immediate alagic response to a substance to which the body has become intensively sensitized
Lubega
different between drug and medicine
ado Reply
drugs have no medical application (cocaine, heroin, crystal meth). medicine have medical purpose (fentanyl, albuterol, aspirin, ect ect)
Jordan
medicine is a substance or preparation used in treating disease,drug is chemical compound medicine are drugs but all drugs are not medicines
Wafa
assalam o alaikum
Sidra
what happen to ECF and ICF regarding to OEDEMA
Zwanga Reply
what are the smooth muscles of the heart
Sintung Reply
stomach
Sidra
identify external features of kidney
saba Reply
kidney weight on males?
saba
and female ?
saba
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Samim
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Samim
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saba
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saba
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saba
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saba
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saba
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saba
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mbbs
saba
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Shahab
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saba
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Shahab
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saba
Define cranial nerves with oder
Javid
O-olfactory O-optic O-occumulator T-trochlear T-trigemenal A-abducent F-facial A-auditory G-glossopharyngeal V-vagus A-acessory
Aniee
opd mean?
Shahab
out patient department
mahesh
thnxx
Shahab
Ty Aniee singh
Javid
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Areeej
Read KD Tripathi book of Pharmacology.
mayank
Hello
mayank
CT Scan means
Sintung
what's health?
Sintung
hello
Philip
hi
Sintung
CT means - computerized tomography
Vivek
connective tissue
Dee
they link some body organs
Sintung
Difference between drug and medicine
Javid
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saba
what is tomography?
Gideon
tomography ☝
shahid
yes
Gideon
how hemolytic anemia cause due to gas gangrene?
Huma Reply
what's gangrene?
Sidra

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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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