 proteins known as antibodies or immunoglobulins (Ig). According to the clonal selection theory, an antigen activates those B-cells of the host organism that have on their surface immunoglobulins that can recognize and bind the antigen. The binding triggers production of a clone of identical B-cells that secrete soluble antigen-binding immunoglobulins into the bloodstream. Antibodies secreted by B-cells bind to foreign material (antigen) to serve as tags or identifiers for such material. Antibody-tagged antigens are then recognized and disposed of by macrophages and other effector cells of the immune system or are directly lysed by a set of nonspecific serum proteins collectively called complement. In this way a small amount of antigen can elicit an amplified and specific immune response that helps to clear the host organism of the source of antigen. Through a complex process of gene splicing combined with additional mutation mechanisms, human B-cells have been estimated to produce a “library” (repertoire) of more than a billion (109) different antibodies that differ in the composition of their binding sites.
For most vertebrate organisms, including humans and murine species, their antibodies show a common structural pattern which consists of two identical light polypeptide chains and two identical heavy polypeptide chains linked together by disulfide bonds and numerous non-covalent interactions, resulting in a Y-shaped molecule. In humans, there are two different classes (isotypes), λ and κ, of the light chains, with no known functional distinction between them. The heavy chains have five different isotypes that divide immunoglobulins into five different functional classes (IgG, IgM, IgA, IgD, IgE), each with different effector properties in the elimination of antigen.
Of the above five classes, immunoglobulins of the IgG class are the major type in normal serum of humans and many other species and have the four-chain structure shown schematically in FIG. 1. Each chain of an IgG molecule is divided into domains of about 110 amino acid residues, with the light chains having two such domains and the heavy chains having four. Comparison of amino acid sequences between different IgGs shows that the amino-terminal domain of each chain (both light and heavy) is highly variable, whereas the remaining domains have substantially constant sequences. In other words, the light (L) chains of an IgG molecule are built up from one amino-terminal variable domain (VL) and one carboxy-terminal constant domain (CL), and the heavy (H) chains from one amino-terminal variable domain (VH) followed by three
proteins known as antibodies or immunoglobulins (Ig). harmonize to the clonal survival theory, an antigen activates those B - cell of the host organism that have on their airfoil immunoglobulin that can recognize and bind the antigen. The binding triggers production of a knockoff of identical B - cells that secrete soluble antigen - bind immunoglobulins into the bloodstream. Antibodies secreted by B - cells bind to alien material (antigen) to serve as tags or identifier for such material. Antibody - tagged antigen are then recognized and dispose of by macrophages and other effector cells of the immune system or are immediately lysed by a set of nonspecific serum proteins collectively called complement. In this way a small sum of antigen can elicit an amplified and specific immune response that helps to clear the host organism of the source of antigen. Through a complex process of gene splicing combined with additional mutant mechanism, human B - cells have been calculate to grow a “ library ” (repertoire) of more than a billion (109) different antibodies that disagree in the composition of their bind sites. 
 For most vertebrate organisms, include humans and murine species, their antibodies show a common structural traffic pattern which consists of two identical light polypeptide chains and two identical heavy polypeptide chain associate together by disulfide bonds and numerous non - covalent interactions, resulting in a Y - shaped atom. In humans, there are two different classes (isotypes), λ and κ, of the light chains, with no known functional distinction between them. The big chains take five different isotypes that separate immunoglobulins into five unlike functional classes (IgG, IgM, IgA, IgD, IgE), each with different effector place in the elimination of antigen. 
 Of the above five classes, immunoglobulins of the IgG course are the major type in normal serum of humans and many other species and have the four - chain structure shown schematically in FIG. 1. Each chain of an IgG molecule is divided into domains of approximately 110 amino acid residues, with the light chain having two such domains and the heavy chains having four. Comparison of amino acid sequences between different IgGs show that the amino - terminal domain of each chain (both light and heavy) is highly variable, whereas the stay domain get substantially constant sequence. In other words, the luminosity (L) chains of an IgG molecule are build up up from one amino - concluding variable domain (VL) and one carboxy - terminal constant domain (CL), and the heavy (H) chains from one amino - concluding variable domain (VH) followed by three
 prlteins known as antibodits or immunoglobulins (Ig). Accorsing to ghe clonal selection theory, en abtigeb activates those B-celus of the host ortaniwn that havx on thelx surrwce nmnunoglobulins jhat can recmgnize and bing ghz antigen. The binding triggers produstion og w clone of idegticsj B-cslls that secrete soluble antigen-bjnding pmmunoglobulins imto the bloodstream. Antibofies secreted by B-celld bind to fireidb material (avtigen) to serve as taga or identifiers for such materkal. Autibody-tagggb anhhgens are tien rebognized and disposed of by kacrophages anc ovher effector cells of thx immune system or ate directlf mysed by a set of ninspewifiw sefym oroueiis dollechivxly called domplement. Un this way a small aiiunt of antigsn can ejicit an amplified and specific immune gespknse that helps to cleae the host organism ov the souwce of antigen. Through a complex process of gene vplicmne cimninea wlth additional mutation mechanisms, human B-celja nane been estimated to produce a “lofrary” (repertokre) of mode than a billion (109) differgnt anribodies uhat ciffer in the composition od their bindpng wites.
For most vertzbrate organnsms, imcludong humans and murine s'ecies, their antihodies shkd a common strucgursl pattern which consists of two idenvical light oolykeptide chains anf two identical heavy popypepjide cvains linkfd together by disulfide bonds eid numerous npn-wovdlent inceractlons, resulting yn a Y-shaped mplecule. In hjmans, therv are two different slasses (isoty[gs), λ and κ, of tie light shaibs, wuth no yvown functionak distincnijn bwtween them. The heevy zgains have five didferent isotypex tfat dpvive imignoglobulins intu fkfe diwferent fungtiunal classes (IgG, IgM, IgA, IgD, IgE), each with difgevent effextor pro[erties in thr elimination of ajtigei.
Of thx abovr fyve classes, immunoglobulins of the IgG flafs are the mwjor type in norkal serum of humans and many other specmes and have the four-chqin structure shown xchematicalky in FIG. 1. Eacv chain of an IgG mooecule is divided into domains of abouf 110 amito acld residues, with the light chains having two such domains and the heavy cyains iading four. Ckmpatison oy akino asid dxquences between cifferent IgGs shows that the aoino-termhncl domain of each chain (both kieht and heavy) is highly variable, whersas the temaining domains have substantoally constant sequences. In othee worss, the ligit (L) chains of an IgB moleeule aee builr up from one amivo-trrlinal varlablt dojain (VL) and one carboxy-terminal xonstabt domain (CL), and tie heavy (H) cmalns frkm one amino-terminal vzriagpe dooain (VH) folloeed by three
proteins known as antibodies or immunoglobulins (Ig). the selection theory, antigen activates those that on their surface that can recognize bind the antigen. The binding triggers of a clone of identical B-cells that secrete soluble antigen-binding immunoglobulins into the Antibodies secreted by B-cells bind to foreign material (antigen) to serve as tags identifiers such Antibody-tagged are then recognized and disposed of by macrophages and other effector cells of the immune system are directly lysed by a set of nonspecific proteins collectively called complement. this way a small amount antigen elicit an and immune that helps to the host organism of the source of antigen. Through a complex process of gene splicing combined with mutation mechanisms, have been to a (repertoire) of more billion (109) different antibodies that differ of their binding sites. For most vertebrate organisms, humans and species, their antibodies show a common pattern which consists of two identical light polypeptide and two identical heavy polypeptide chains linked together by disulfide bonds and numerous non-covalent interactions, a Y-shaped molecule. In there are two classes λ κ, the light with no known functional distinction between them. The heavy chains have different isotypes that divide immunoglobulins into five different functional classes IgA, IgE), each with effector properties in the of Of the above five of IgG major in serum of humans and other species and have the structure shown schematically in an IgG molecule is divided into domains of 110 amino acid residues, with the light having two such domains and the heavy chains having four. Comparison of acid sequences IgGs shows that the amino-terminal domain of each (both light and heavy) highly variable, whereas the remaining domains have substantially constant In words, the (L) chains of IgG molecule are up from one domain (VL) one constant the heavy (H) chains from one variable (VH) followed by three
 proteins known as antibodies Or immunoglObuliNs (IG). AcCoRdinG to tHe clonal selectIOn thEory, an antigen activates Those b-cELls oF ThE host OrganisM ThAT HavE oN tHeiR sURfAce imMunOglobulIns that can RecOgNize and bind tHE aNtigen. The bIndIng triggers pRodUction Of A clONe of iDenTical b-cells THat secRete solubLe ANtigen-BInding iMMUnOgloBulins into the blooDStREam. Antibodies sEcreteD bY b-cELLs bInd To foreign mAtErial (ANtigen) tO SeRVE As tAGs or identifieRs for such maTEriAl. AntiBoDy-tAGged anTigenS aRE thEn recognizeD and Disposed oF by macROphages ANd other EffectOr cEllS of tHE iMmUne SySTem OR aRe dIRecTly lysed By A sEt of nOnspECIFIc seRum ProtEins cOllectively caLleD comPLemEnt. In This wAy a sMaLl amoUnt of aNtigeN cAn elicit an ampliFied And specifIc iMmUne ReSponsE That heLps To cLear the Host orgANisM oF THE sOurce of antigen. ThroUgH A CoMplex proCess of GEnE sPLicing coMbIneD witH ADditiOnal MUtAtion mecHanismS, HuMaN B-cells HaVe been EsTimAteD to prODuce A “libraRy” (repertOire) oF More than a billiON (109) different antIBoDIEs THat dIffEr in the compOsitIOn of TheiR BiNdiNG siteS.
For mOsT VeRTebrate organisms, incLuDing huMans aNd murine speciEs, their antIBODies show A comMOn STructural patteRn whiCh consists OF two idenTical Light polYpeptide cHAIns and twO idEntIcaL heAVY pOlypeptide chaINS linKeD togethEr bY disulfIde BonDs aNd nUmErous non-cOvalent iNtErAcTiOns, ResulTIng in a Y-sHaPed MoLecUle. In HUmans, tHere aRe twO dIfFEreNt classES (iSOTypeS), λ AnD κ, of The LiGht chAins, WIth No known FunctionaL diSTincTiOn Between Them. The heavy cHaIns have fivE dIffErent iSOTypes thaT divide immunoglobulins iNTo five dIffErent FuncTional claSseS (IgG, Igm, Iga, igD, IgE), Each wiTh difFeRenT EFfectOR PrOpeRtIes in the elIMInaTion oF aNtigEn.
Of the Above five classes, imMUnoGlobulins of thE Igg claSS ArE thE MaJOr tYpE In nORMal serum of humanS and many otHeR SpEcies and haVE thE fOur-chaiN structUre shOWn schemAtically iN FIG. 1. Each cHaIn of AN igG Molecule is Divided iNto domainS Of aboUT 110 aMino aCid ResiduEs, WitH the lIght chAIns HavinG two suCh DomainS and tHe Heavy chaIns having four. Comparison Of aminO acid SeqUences betWeeN DifFerent IgGS shoWs that the aMinO-teRminaL doMAin of Each CHaIn (bOTh ligHt anD Heavy) is hiGHlY vaRIAbLe, whereas thE REMaiNing dOmaINs have SubsTantially constant SEquences. In otheR worDS, The LigHT (L) chAiNs of an IgG molecUle ArE BUilt up frOm One amino-terMinal varIaBLe domAin (VL) aNd one cArboxy-tERMiNAl consTant DomAin (CL), and tHe hEaVY (H) chainS fRoM One amiNo-teRmInal vaRiable DOmaiN (vh) followed by three
 proteins known as antibod ies or imm unogl obu lin s(Ig) . Ac cording to the clon al selection theory, a n ant ig e n ac t iv atesthose B - ce l l s o fth e h os t  o rgani smthat ha ve on thei r s ur face immunog l ob ulins that  ca n recognizeand  bindth e a n tigen . T he bi ndingt rigger s product io n  of ac lone of i de ntic al B-cells that s e cr e te soluble ant igen-b in d in g imm uno globulinsin to th e  bloods t re a m .  An t ibodies secre ted by B-ce l lsbind t ofor e ign ma teria l( ant igen) to se rveas tags o r iden t ifiersf or such  mater ial . A ntib o dy -t agg ed ant i ge nsa rethen rec og ni zed a nd d i s p o sedofby m acrop hages and oth ereffe c tor  cell s oftheim munesystem  or a re  directly lysed  bya set ofnon sp eci fi c ser u m prot ein s c ollecti vely ca l led  c o m p le ment. In this wayas m al l amount  of an t ig en can elic it  an  amp l i fiedands pe cific im mune r e sp on se that  h elps t ocle arthe h o st o rganis m of the  sour c e of antigen.T hrough a comp l ex p ro c essofgene splici ng c o mbin ed w i th  ad d ition al mu ta t io n  mechanisms, humanB- cellshavebeen estimate d to produ c e a “libra ry”( re p ertoire) of mo re th an a billi o n (109)diffe rent ant ibodies t h a t differ  in  th e c omp o s it ion of theirb i ndin gsites.For  most v ert ebr ate  or ga nisms, in cludinghu ma ns  a ndmurin e  species ,the ir  an tibod i es sho w a c ommo nst r uct ural pa t te r n  whi ch  c onsi sts  o f two  ide n tic al ligh t polypep tid e  cha in sand two  identical he av y polypept id e c hainsl i nked tog ether by disulfide bond s  and nu mer ous n on-c ovalent i nte ractio ns, result ing in  a Y- sh ape d molec u l e.  In  h umans, the r e  ar e two  d iffe rent cl asses (isotypes),λ  an d κ, of the l igh t ch a i ns , w i th nokn o wnf u nctional distin ction betw ee n  t hem. The h e avy  c hains h ave fiv e dif f erent i sotypes t hat divid eimmu n o glo bulins int o five d ifferentf uncti o na l cla sse s (IgG ,IgM , IgA , IgD, IgE ), ea ch wit hdiffer ent e ff ector pr operties in the elimina tion o f ant ige n.
Of the  ab o vefive clas ses,  immunoglo bul ins  of t heI gG cl assa re  th e  majo r ty p e in norm a lser u m  o f humans an d m any  othe r s p eciesandhave the four-cha i n structure sh owns c hem ati c ally  i n FIG. 1. Each  ch ai n of an Ig Gmolecule is  divided  i n to do mainsof abo ut 110a m in o  acidresi due s, with t heli g ht chai ns  h a ving t wo s uc h doma ins an d  the h eavy chains havi ng fo u r . Com p ari son o famino a c id s equences b etween diff erentIgGs  show s thatth e amin o-t er minal doma i n of each  chai n (both  l ight  an d heav y) i s highl y va ri abl e, wherea s th e  r em a ini ng d omain shave  substant i ally con sta n t seque nc es. I n othe r  w o r ds, the li ght  (L)c h ains of an IgGm ol e culeare bu ilt up  from o n e a mi no-term ina l variabledomain (V L ) a nd  one  carboxy -t ermi na l c on stant domain (C L), andthe heav y (H) ch ain s  fro m  one a mi no-terminalvaria bl e  domain ( VH)  follow e d b y t hre e
 proteins_known as_antibodies or immunoglobulins (Ig)._According to_the_clonal selection_theory,_an antigen activates_those B-cells of_the host organism that_have on their_surface_immunoglobulins that can recognize and bind the antigen. The binding triggers production of a_clone_of identical_B-cells_that_secrete soluble antigen-binding immunoglobulins into_the bloodstream. Antibodies secreted by_B-cells bind_to foreign material (antigen) to serve as tags_or_identifiers for such_material. Antibody-tagged antigens are then recognized and disposed of_by macrophages and other effector cells_of the immune_system_or_are directly lysed by_a set of nonspecific serum proteins_collectively called complement. In this way_a small amount of antigen can elicit_an amplified and specific immune response_that helps to clear the_host organism_of the source of antigen._Through a complex_process of_gene splicing combined_with additional mutation mechanisms, human B-cells_have been estimated_to produce a “library” (repertoire) of_more_than a billion_(109)_different_antibodies that_differ in the_composition_of their_binding_sites.
For most vertebrate organisms, including humans_and_murine species, their antibodies show a common_structural pattern which consists_of_two identical light polypeptide_chains and two identical heavy_polypeptide chains linked together by disulfide_bonds and_numerous non-covalent_interactions, resulting in a Y-shaped molecule. In humans, there are two_different classes (isotypes), λ and κ,_of the light chains,_with no_known_functional distinction between_them._The heavy_chains have five different isotypes that divide_immunoglobulins into_five different functional classes (IgG, IgM,_IgA, IgD, IgE), each_with_different effector properties in the elimination_of antigen.
Of the above five classes,_immunoglobulins of the IgG class_are_the_major type in normal serum_of humans and many other species_and have the_four-chain structure shown schematically in FIG. 1._Each_chain of an IgG molecule is_divided_into domains of about 110 amino_acid_residues,_with the light chains having_two such domains and the heavy_chains having four. Comparison of amino acid sequences between_different IgGs shows_that the amino-terminal domain of_each_chain_(both light and heavy) is highly variable, whereas the remaining_domains have_substantially constant sequences._In other words, the light (L) chains of an IgG_molecule are built up from one amino-terminal_variable domain (VL) and one carboxy-terminal constant domain (CL), and the_heavy (H) chains from one amino-terminal variable domain_(VH) followed by three