科学知识

Virus causing illness in humans


1.Respiratory Syncytial Virus (RSV)

Respiratory syncytial (sin-SISH-uhl) virus, or RSV, is a respiratory virus that infects the lungs and breathing passages.
Healthy people 
usually experience mild, cold-like symptoms and recover in a week or two. But RSV can be serious, 
especially for infants and older adults. 
In fact, RSV is the most common cause of bronchiolitis (inflammation of the small 
airways in the lung) and pneumonia in children younger than 1 year of age in the United States. In addition, RSV is being 
recognized more often as a significant cause of respiratory illness in older adults.

2.Human Immunodeficiency Virus (HIV)

Human immunodeficiency virus (HIV) is a blood-borne virus typically transmitted via sexual intercourse, shared 
intravenous drug 
paraphernalia, and mother-to-child transmission (MTCT), which can occur during the birth process
or during breastfeeding. HIV disease is caused by infection with HIV-1 or HIV-2, which are retroviruses in the Retroviridae
family , Lentivirus genus.

3.Hepatitis C virus

Hepatitis C virus (HCV) is a small (55–65 nm in size), enveloped, positive-sense single-stranded RNA virus of the family 
Flaviviridae. Hepatitis C virus is the cause of hepatitis C and some cancer lymphomas in humans.

4. Human papillomavirus

Human papillomavirus (HPV) is a DNA virus from the papillomavirus family that is capable of infecting humans. Like all 
papillomaviruses, 
HPVs establish productive infections only in keratinocytesof the skin or mucous membranes. Most HPV
infections are subclinical and will 
cause no physical symptoms; however, in some people subclinical infections will 
become clinical and may cause benignpapillomas (such as warts [verrucae] or squamous cell papilloma), premalignant
lesions that will drive to cancers of the cervix, vulva, vagina,penis, oropharynx and anus. In particular, HPV16 and HPV18
are known to cause around 70% of cervical cancer cases.

5. Rabies virus

The rabies virus is a neurotropic virus that causes rabies in humans and animals. Rabies transmission can occur through 
the saliva of 
animals and less commonly through contact with human saliva.
The rabies virus has a cylindrical
morphology and is the type species of the Lyssavirus genus of the Rhabdoviridae family. These viruses are enveloped
and have a single stranded RNA genome withnegative-sense.
The genetic information is packaged as a ribonucleoprotein
complex in which RNA is tightly bound by the viral nucleoprotein. The RNA 
genome of the virus encodes five genes
whose order is highly conserved. These genes code for nucleoprotein (N), phosphoprotein (P), 
matrix protein (M),
glycoprotein (G) and the viral RNA polymerase (L). The complete genome sequences range from 11,615 to 11,966 nt in
length.



Antibody

 Antibodies are immune system-related proteins called immunoglobulins. Each antibody 
consists of four 
polypeptides–two heavy chains and two light chains joined to form a "Y" 
shaped molecule.The amino 
acid sequence in the tips of the"Y" varies greatly among 
different antibodies. This variable region,
composed of 110-130 amino acids, give the 
antibody its specificity for binding antigen. The variable 
region includes the ends of the 
light and heavy chains. Treating the antibody with a protease can cleave 
this region, 
producing Fab or fragment antigen binding that include the variable ends of an antibody.
The constant region determines the mechanism used to destroy antigen. Antibodies 
are divided into 
five major classes, IgM, IgG, IgA, IgD, and IgE, based on their constant 
region structure and immune 
function.








The interaction of antibody molecule with specific antigen


Localized regions of hypervariable sequence form the antigen-binding site.
Three particular variable segments can be identified in both the VH and VL domains. They are designated hypervariable 
regions and are 
denoted HV1, HV2, HV3. The regions between the hypervariable regions, which comprise the rest of the 
V domain, show less variability 
and are termed the framework regions. There are four such regions in each V domain, 
designated FR1, FR2, FR3, and FR4. 
When the VH and VL domains are paired in the antibody molecule, the hypervariable
loops from each domain are bought together, creating a 
single hypervariable site at the tip of each arm of the molecule. 
This is the binding site for antigen, the antigen-binding site or antibody 
combining site. The six hypervariable loops 
determine antigen specificity by forming a surface complementary to the antigen,and are 
more commomly termed the 
complementarity-determining regions, or CDRs.  
 


Antibodies bind antigens via contacts with amino acids in CDRs, but the details of binding depend
upon the size and shape of the antigen.

In general, the substances found to bind to these antibodies were haptens, such as phosphorylcholine or vitamin K1. 
Structural analysis 
of complexes of antibodies with their hapten ligands provided the first direct evidence that the 
hypervariable regions from the antigen-
binding site, and demonstrated the structural basis of specificity for the hapten. 
Subsequently, with the discovery of methods of 
generating monoclonal antibodies, it became possible to make large 
amounts of pure antibodies specific for many different antigens. 
This has provided a more general picture of how 
antibodies interact with their antigens, confirming and extending the view of antibody-
antigen interactions derived from 
the study of haptens.


Antibodies bind to conformational shapes on the surfaces of antigens.
Some of the most important pathogens have polysaccharide coats, and antibodies that recognize epitopes formed by 
the sugar subunits 
of these molecules are essential in providing immune protection from such pathogens. In many cases,
however, the antigens that provoke 
an immune response are proteins. For example, protective antibodies against viruses 
recognize viral coat proteins.


Antigen-antibody interactions involve a variety of forces.
The interaction between an antibody and its antigen can be disrupted by high salt concentrations, by extremes of pH, by 
detergents, 
and sometimes by competition with high concentrations of the pure epitope itself. The binding is therefore 
a reversible noncovalent 
interaction.