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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

study about internal structure, outer structure and their functions
Navdeep Reply
circulatory system on blood pressure
Lakhu Reply
What is ELISA
POULAMI Reply
(enzyme linked immunosorbent assay) is a test that uses antibodies and color change to identify a substance.
luke
tr
Mohamed
what's defense mechanism?
Saintina
psychological strategies that are unconsciously used to protect a person from anxiety arising from unacceptable thoughts or feelings.
Henry
difference between apocrine sweat glands and merocrine sweat glands
Binkheir Reply
I believe the apocrine sweat gland uses a sac under the hair follicle and the merocrine sweat gland releases directly on to the surface of the skin
Mark
normal blood volume in our body
pankaj Reply
5Litres
Albert
Normal blood volume in adults is 6 litres
Kedha's
4.7 to 5ltr.. normal for adult
Clangbhelle
what are the advantages of the concave shape of red blood cells?
Amy Reply
This structure is VERY flexible. It can allow these cells to get into the most tiny places in our bodies. a VERY good design! The advantage of red blood cells' biconcave shape is that the surface area is increased to allow more haemoglobin to be stored in the cell.
Saafi
They can stack so that they can move to capillaries
Nejat
action of gluteus medius and minimus
Green Reply
Lateral rotation of the hip joint
Hertzo
Briefly explain location of ecg on a patient
Prince Reply
it is a machine that gives a graphical representation of heart beat
Nani
Briefly explain location of ecg leads on a patient?
Prince
in ecg we use electrical leads over the chest ,ancle and wrist
Nani
what is the anatomical and function difference between paravertebral and prevertebral ganglia ?
Rada Reply
types of tissue in human
Preety Reply
charactetistic Of cartilaginous tissue
Preety
what is theRecurrent infection?
pankaj Reply
what do you mean about recurrent infection
pankaj
Recurrent or persistent infection is a manifestation of primary immuno deficiency
Kedha's
weakens the immune system, allowing infections and other health problems to occur more easily
Kedha's
lysis of RBC
Abdirizack
What is barometric pressure
Kedha's Reply
what is the agglutination advantage
Gopal Reply
the functions of the liver
Nana Reply
it produces bile juice which is used to make the food smaller
Kedha's
it also plays an important role in conversion of amino acid into urea
Komal
it also has role in gluconeogenesis in which amino acids and lipids convert into glucose.
Komal
during fetal life it's a center for hemopoiesis (formation of blood cells)
Komal
it filters, or removes, harmful substances from the blood
Kedha's
It stores nutrients, such as vitamins and iron,for the body
Kedha's
what is the largest gland in human body
Shahid Reply
liver
rachna
correct
Said
correct
dominic
thyroid gland
Kedha's
thyroid is largest endocrine gland
Komal

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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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