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Antigenicity Rao S S - Indian J Ophthalmol
 
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ARTICLES
Year : 1972  |  Volume : 20  |  Issue : 2  |  Page : 42-44
 

Antigenicity


Haffkine Institute, Bombay-12, India

Correspondence Address:
S S Rao
Haffkine Institute, Bombay-12
India
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PMID: 4128682

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How to cite this article:
Rao S S. Antigenicity. Indian J Ophthalmol 1972;20:42-4

How to cite this URL:
Rao S S. Antigenicity. Indian J Ophthalmol [serial online] 1972 [cited 2014 Mar 7];20:42-4. Available from: http://www.ijo.in/text.asp?1972/20/2/42/34671


The term 'antigenicity' has been used to describe both the ability of the antigen to combine with the antibody and also its ability to in­duce antibody formation. In recent years however, the first property of the antigen is called antigeni­city and the second immunogeni­city. This is because some small molecules for which the immuno­logists use the term 'haptens' are capable of combining with antibody but are unable to elicit anti­body formation. The combining group of the antigen is called the "determinant group". The haptens can however be made immunoge­nic by attaching them to certain immunogenic carrier molecules. Antibodies reacting with penicillin can be produced by tagging it to serum albumin. Antibodies can thus be produced to any simple substance. There are substances called "adjuvants" which are not immunogenic by themselves but can enhance antibody production of weakly immunogenic substances. These are important in vaccina­tions to enhance antibody reponse. Aluminium hydroxide used in alum precipitated vaccines is an exam­ple of an adjuvant. There are also substances called immunosuppres­sors which suppress the immune response. They are important in autoimmune disease and in pre­venting rejection of homograft. Hydrocortisone is an important immuno supressor.

Synthetic Antigens

In the last few years immuno­genicity has been studied using synthetic polypeptides of known structure and interesting facts have come to light. It was the pre­vailing belief among immunolo­gists that only large macromole­cules of molecular weight over 6.000 could be immunogenic. This was because insulin and gelatin which have a molecular weight of about 6000 are not immunogenic normally. Recent work has shown that polypeptides of single amino­acids say poly-L-lysine even though they may have molecular weight of over 50.000 are still not antigenic in any species of animals. However, polylysine with only 7 or 8 units to which is attached a single dinitrophenyl group is im­munogenic in guinea-pigs giving rise to both antibody production as well as cellular immunity as in­dicated by the delayed skin sensi­tization to the polypeptide. The smallest substance which can elicit antibody production in guinea-pigs is N-acetyl-L-Tyrosine-azo-phenyl arson ate which has a molecular weight of only 450.

A large immunogenic molecule may have one or more determi­nant groups which have structures foreign to the host. In such a case specific antibodies are formed to each of the determinant groups which are on the surface and therefore accessible. Hidden deter­minant groups may not be im­munogenic.

The nature of the antigen and its dosage are also important for immunogenicity. Polymerised an­tigens are more immunogenic than their monomers. Repeated administration of very low doses or very high doses can produce im­munoparalysis while intermediate doses may be immunogenic. For example. Mitchison has reported that bovine serum albumin is im­munizing when injected in dose of 10 -7 to 10 -6 moles in mice but is par­alysing when low doses of 10 -8 moles or below or high doses of 10 -5 or below or high doses of 10 -5 moles and above are injected. No detectable antibodies are produc­ed when injected with a paralytic dose. Introduction of the unnatu­ral D-amino acids in the molecule reduces immunogenicity and even small doses may lead to paralysis. The optical configuration of the amino acids is therefore impor­tant.

The three dimentional structure is most important both for anti­genicity and immunogencity. The antibodies produced are specific to the three dimentional structure. Antibodies produced to a short linear (straight chain) sequence of amino acids are different in their specificity or combining activity to antibodies produced to the same sequence of amono-acids but having a helical structure. Very slight changes in the position of individual groups in a mole­cule or its spacial conformation alter profoundly the specificity of the antibody formed.

The immunogenicity depends also on the species and the strain of the animal used. For example, purified pneumococcal polysaccha­rides, prepared from the capsular material of pneunuococci, are not at all immunogenic in rabbits. In­tact pneunococci nave to be inject­ed to produce the antibodies which will then react with the purified polysaccharide. However, purified polysaccharides are high­ly immunogenic in mice, rats and men and antisera will show strong agglutination with the whole or­ganisms also. When pure inbred strains of mice or guinea pigs were immunized with synthetic polypeptides of known structure, certain interesting facts emerged. Some strains of animals responded to particular structure and other strains did not respond. For exam­ple, strain 2 of guinea-pigs produc­ed antibodies when immunized with dinitrophenyl poly-L-lysine (DNP-PLL) while strain 13 did not produce any antibody. Breeding experiments showed that response to DNP-PLL is due to the so called PLL gene which is present in strain 2 and not in strain 13. Cross breed­ing experiments showed that this gene is autosomal and dominant. Later, it was found that the res­ponse to copolymer of L-glutamic acid and L-tyrosine (GT) is the property of the strain 13 and not of the strain 2. Thus the GT gene is present in strain 13 and not in strain 2. Very recent work indicates that the genes con­trolling immunogenicity in any given species or strain may be fairly large and some of them may be linked to histocompatibility genes of these strains. Similar work has been done with the im­mune response genes in the diffe­rent strains of mice. Vigorous work is going on at present to identify the genes controlling the immune response and map them on particular chromosomes.



 
 
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