Virus causing illness in humans
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)
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
Flaviviridae. Hepatitis C virus is the cause of hepatitis C and some cancer lymphomas in humans.
4. Human papillomavirus
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 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
■ 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.
detergents, and sometimes by competition with high concentrations of the pure epitope itself. The binding is therefore
a reversible noncovalent interaction.