Fundamental principles of immunization (1961)

for when in 1797 Jenner inoculated the arm of James fips A young boy of eight with the contents of a cpox bleb from a dairy Ma and in the following year published his work on vaccination against small poox it became possible for the first time to protect human beings artificially against pathogenic organisms to immunize them and a new era in preventive medicine had begun in Jenner's day when the population of Great Britain was about 10 m ion most people hope to catch small Parks only in its milder form in order to gain protection against an epidemic of the sever kind even so in 1796 one death in every five was due to small pox today vaccination has completely changed the picture for example in 1958 with a population of 50 million there were six cases and one death it is now except for imported cases leading to local epidemics a comparative Rarity and will remain so so long as vaccination is sufficiently widely practiced similar considerations apply to other diseases but to understand how immunity can be acquired either naturally or artificially we must first consider certain basic principles if a foreign substance such as a protein enters the body of a man or other animal there is an active response by the production of a specific antidote which neutralizes the toxic effects of the protein as a preliminary to its elimination invading foreign substances which act in this way are termed antigens and the neutralizing substances they give rise to antibodies this antigen antibody reaction also operates when pathogenic microorganisms attack the body since the toxic effects of these are likewise due to protein like substances either contained in or released by them with invading bacteria and viruses however the situation is more complicated than this simple picture might convey since these are living organisms with their own differing characteristics in virus infections for instance such as poliomyelitis in man and distemper in the dog the virus itself is the antigen which stimulates the formation of antibody in some bacterial infections such as anetic fevers and hooping cough in man and Anthrax and coliform infections in animals the organisms invade and multiply in the host the accumulation of bacterial growth is toxic and constitutes the antigen the protecting antibody that is formed is one that prevents this multiplication in another important class the bacteria May remain localized but release a powerful toxin which diffuses into the bloodstream in such [Music] exotoxin deia and tetanus and lamb dentry and pulpy kidney disease of sheep it is the toxin which is the important antigen since bacteria belonging to this class are in some respects more clearcut in their behavior than other bacteria and viruses it is convenient to discuss them in more detail first let us assume that a completely unprotected that is to say a susceptible or non-immune person or animal becomes infected with a Vigilant organism belonging to this class as we have said toxin producing bacteria May remain localized but release a powerful toxin which diffuses into the bloodstream to attack a number of vital centers it is this toxin which is the important antigen and as in the case of the protein the body cells respond actively by the production of antibody if in the untreated subject the body cells produce enough antibody or antitoxin as it is called in this case rapidly enough to neutralize the toxin before irreversible damage has occurred recovery will follow antitoxin will then predominate as a result of a clinical attack of a bacterial dis disease the status of the subject is in many cases changed from non-immune to immune though the concentration of antibody in the blood may drop after the lapse of time when it is no longer needed what has happened is that the body has become trained as it were in the mechanism of its production and a pattern for the rapid Reformation of fresh antibody persists represented here by these blue ringed circles sometimes even repeated subclinical infection will produce a simp SAR result and should a further attack be experienced the body will almost always produce antibodies sufficiently rapidly and in such quantity that clinical symptoms are unlikely to appear immunity acquired in this way by reaction of the body itself is called active immunity and when naturally conferred by an attack of some but not all infectious diseases is fairly solid a more lasting immunity than that following an attack can can as a general rule be induced by artificially stimulating the production of antibody such as antitoxin into a non-immune person or animal we can inject what is called a toxoid which is in fact toxin rendered non-toxic and therefore harmless by chemical treatment for example with formalin but which is sufficiently like toxin to retain the capacity to stimulate the body to produce antitoxin a single injection of toxoid or one of its derivatives which may sometimes be used is seldom sufficient to produce measurable immunity but will educate the body to respond quickly and efficiently to a subsequent stimulus the antitoxin produced appears in the blood serum and is measurable in this way it can be established that a single injection of for example one of the potent defia prophylactics results at Best in a very low level of antitoxin which even at its maximum after 4 to 6 weeks is well below that required to confer protection such a minimal or Primary Response has resulted from what is called the primary stimulus if however a secondary stimulus is given at a suitable interval after the Primary Response a secondary response ensues in in which a comparatively High concentration of antitoxin is produced in the blood serum the concentration reaching its maximum about 10 days after the injection and thereafter falling off relatively slowly a high degree of immunity can be induced in this way though with time it gradually Falls by reinforcing doses given from time to time however it is capable of Rapid restoration the phenomenon of primary and secondary stimulation was discovered by Glenny and sudon in the welcome Research Laboratories in 1921 and today forms the basis of all accepted methods of immunization with toxins or their toxoid derivatives again as occurs in many cases with recovery from a natural attack the inoculated subject is now actively immune again the pattern for the rapid Reformation of antitoxin is present but as we have seen the basic Community which enables this to happen takes time to develop but there are many occasions for example when a non-immune person or animal is exposed to heavy infection when there is no time to allow the comparatively slow processes of active immunization in such cases antitoxin is urgently required and Resort must be had to direct injection of blood serum containing antitoxin in enough quantity to neutralize the toxin as it develops to protect such antitoxin must be injected promptly and is in fact best used at the earliest possible moment after exposure to infection serum containing antitoxin for use in this way is also called anti-serum and is usually produced in a horse a particularly suitable animal for this purpose the protection afforded is however shortlived since the serum not being produced by the subject's own body and thus being a foreign protein is eliminated comparatively rapidly temporary immunity conferred in this way by injecting antibodies is called passive immunity and can be contrasted with the active immunity produced by inoculation with antigens such as toxoids passive immunization is ready made help inting disease in which the body plays only a passive role it is rapid in onset but of short duration active immunization on the other hand is a means of training the body to protect itself by its own activity it takes an appreciable time to develop but is long-lasting this difference between active and passive immunity is fundamental it is important to remember however that immunity either active or passive to one disease caners no protection against other completely unrelated diseases there are then these two basic types of immunity active and passive to recapitulate active immunity may be acquired Naturally by recovery from an attack of disease or by subclinical infection preferably active immunity may be induced artificially by inoculation with an antigen in all active immunity the subject's body itself is trained to produce antibody and Immunity is slow to develop lasting in character and when it falls generally capable of Rapid restoration passive immunity may be conferred by inoculation with antibody produced outside the patient and in this case immunity develops rapidly but is transient in character although so far we have only discussed exoxtic bacterial infections these principles nevertheless are capable of more General extension though there are as might be expected variations and exceptions from disease to disease as well as between the different classes of disease before drawing attention to some of the variations however we must first consider certain practical consequences which arise out of the basic principles as we have said antiserum for Passive immunization is usually produced in a horse after a period of isolation and other essential preliminaries the animal undergo an intensive course of active immunization by repeated inoculations with antigen in this way it is brought to what is termed a hyperimmune state in which the blood serum is rich in antibody periodic bleedings from the jugular vein are then taken this procedure can adopted for the preparation of anti-era for Passive immunization against various bacterial infections after bleeding the antiserum is refined and concentrated as we have already said horse serum when injected into a different species constitutes a foreign protein which is eliminated more or less rapidly and it is for this and other reasons including the risk of undesirable serum reactions that concentration in plant like this to bring the ratio of one wanted antibody to unwanted serum protein to the highest possible level is important in the case of antitoxic C such as that of defia for example the antitoxin bearing fraction can as we see here be separated by a proc process involving pepsin treatment at a controlled pH this is followed by heat denaturation and precipitation of the purified antitoxin in the filtrate with ammonium sulfate the precipitated cake contains the desired fraction the ammonium sulfate is subsequently removed from the precipitate by Dialysis in cellophane sex to describe the process as briefly as this is of course to oversimplify but the details are less important than the reasons for concentration to separate pure antibody however remains a practical impossibility however carefully they are concentrated antier prepared from the horse always contain some unwanted protein in addition to the antibody protein and both are horse serum proteins valuable and important as such products are therefore here tetanus antitoxin is being automatically filled into ampols under completely sterile conditions considerations of this kind suggest that if we wish to take greatest advantage of passive immunization to ensure that the antibodies remain as long as possible in the body of the subject we should make use not of heterologous antia from the horse but of potent homologous antia from the species we wish to protect unfortunately this too is not usually practicable except in the case of some virus diseases in measles for instance blood serum taken from a preferably young patient a week or so after the temperature has returned to normal after a natural attack has a useful value as a passive immunizing agent such anti-serum is called convalescent serum but is obviously not widely available but with the increase in the blood donor service and since people are exposed to many different bacteria and viruses large pools of blood plasma are now available which normally contain a variety of protective antibodies these are located mainly in the gamma fraction of the globulin which can be separated gamma globulin from pulled adult plasma has been recommended for the passive immunization of susceptible contacts against some virus diseases such as measles rubella and poliomyelitis but has been stated to be ineffective against others such as mumps or chickenpox in some cases gamma globulin containing more more specific antibodies such as that prepared from the blood of persons recently vaccinated against small poox is of value or for example a dog the owner of which has failed to have it actively immunized may be protected for a period against canine distemper by passive immunization with antiserum prepared from the blood of another dog actively immunized against the disease in all such cases since the serum is homologous the body is less prone to reject it hurriedly and the protection conferred is somewhat longer lasting than is possible with heterologous antisera we thus have a further important principle passive immunity can be conferred either by use of heterologous antia prepared usually in the horse or by use of homologous antisa prepared in the same species with heterologus antisera the protection conferred is relatively brief since they contain forign protein which is rapidly eliminated with homologous antisera on the other hand the protection is somewhat longer lasting in both cases however the effect is only temporary since in any form of passive immunization the body itself is in no way trained to produce its own antibody the protection conferred therefore is markedly inferior to that induced by by active immunization but this is not the whole story suppose a woman is actively immunized and that the level of antibody in her blood serum is high suppose now she gives birth to a child the blood serum of the child will also be rich in antibody which in the case of men apes and rodents has been transferred from the mother to The Offspring mainly by means of the permeable placenta this transferred immunity is however passive again the antibody has not been produced by the body of the child itself a similar transference of antibody occurs in certain other mammals but in the case of ulet such as cattle and sheep this takes place not via the placenta which is impermeable in these species but via the colostrum or first milk which is ingested into the gut and from which antibody is absorbed into the bloodstream of The Offspring we thus have have yet another important principle that active immunity in a mother can be transferred as passive immunity to The Offspring but it must be remembered that though transferred by the most homolgous means possible such immunity in the newborn child or animal is still passive in character and is therefore of limited duration from this principle of transferred immunity some important consequences follow for example in hill sheep farming lamb dentry at one time caused losses of up to 40% of the Lambs this disease only attacks within the first few days after birth and plainly sheer inaccessibility May prevent the passive immunization by heterologous antiserum of each lamb immediately it is born while even if practicable active immunization of the Lambs is out of the question since there is no time for the immunity to build up before exposure to infection but by active immunization of the use so enabling the Lambs to be passively protected following the first feed of colostrum the mortality rate from lamb dentry can now be reduced to negligible proportions but there is another side to the picture in protecting dogs against canine distemper for instance where active immunization is affected by use of an attenuated living virus as antigen the presence of transferred maternal immunity May prevent m multiplication of the virus if we attempt to immunize puppies at too young an age for this reason active immunization must be delayed until the transferred passive immunity has faded similar considerations apply to babies born of mothers actively immunized against poliomyelitis in their own interest during or before their pregnancy here too transferred immunity would interfere if an attempt were made to immunize the child actively too early but active immunization nevertheless Remains by far the better way to protect both human beings and animals against infection and should be preferred wherever possible as we have indicated pathogenic organisms may be divided into three broad classes viruses bacteria which invade and multiply in the host and do not produce a soluble Toxin and toxin producing bacteria which last class we have already discussed in some detail and to which defia belongs as we have seen though toxin producing bacteria May remain localized they release a powerful toxin which in a natural attack is in fact the important antigen this however is usually far too toxic for use as an antigen in active immunization instead of this therefore the harmless toxoid or toxoid derivative is employed to prepare the toxoid of course the toxin itself must first be produced by culture of selected strains of the bacteria defia basili for instance may be grown under artificial conditions in a suitable broth to produce a fluid rich in toxin after filtration a suitable concentration of Malahide is added to the crude toxin after which it is transferred to glass bottles for incubation incubation takes 2 or 3 weeks and as a result of this treatment the non-toxic toxoid is formed which produces no unfavorable symptoms when injected into guinea pigs in large doses it is however still antigenic in that it still possesses the property of stimulating the formation of antibody the toxoid is purified in this case the desired fraction is precipitated by ammonium sulfate and is separated by filtration treatment of the respective toxins with formaly is also used for the preparation of other toxoids including those for active immunization against lamb dentry black leg braxi and pulpy kidney disease in animals and tetanus and botulism in man such toxoids are often referred to as formal toxoids where desirable these too may be submitted to a process of purification in some cases such as those of D theia braxi pulpy kidney disease and others the toxoid may be precipitated or absorbed with a preparation of Alum before use this gives a relatively insoluble product which is more slowly absorbed and excreted than formal toxoid itself and which because of this possesses enhanced antigenic efficiency the the original discovery of this use of Alum was made in these Laboratories as with all other biological products toxoids and their derivatives are of course filled into bottles and ampols under completely sterile conditions we have referred to products in this class as toxoids but this term is now less used than forly and is usually applied only to those toxoids intended for active immunization of human beings for all products used to induce active immunity including toxoids for use against animal infections and increasingly those against human infections also the more general term vaccine is being preferred vaccines can also be prepared for active immunization against diseases due to pathogenic bacteria which do not produce a soluble toxin we are therefore unable to obtain a toxoid and recourse must be had for the antigen to the bacteria themselves in the case of hooping C for example bordella petasis may be grown in a special culture medium designed to reduce the amount of unwanted foreign protein in the finished vaccine the medium contained in 2 and 1/2 liter flasks is inoculated with a suspension of the billus after incubation for a suitable period the bacteria are killed with form Malahide vaccines in this class consist in fact essentially of killed bacteria since with the exception of tuberculosis where the well-known BCG vaccine can be used it is not possible to employ living attenuated strains in the human field although there are a few such Veterinary vaccines sampling to test for the purity of the strain centrifuging to separate the killed culture and addition of an antibacterial substance are followed by standardization by adjustment of the opacity of a suspension to a standard value antigenic activity is assessed by making a challenging intrac cerial injection of living culture into aized mice which have been previously inoculated with the vaccine under test active immunization is possible with varying degrees of success against most diseases caused by pathogenic bacteria which do not produce a soluble toxin such as the antic fever group chera and plague in man and poster alosis and Swine Reis in animals here swiis vaccine is under inspection before packing largely because killed bacteria are used however more frequent reinoculation may be required than in the case of infections due to toxin producing bacteria though passive immunization with antisera is of some value in the treatment of certain Veterinary diseases in this class such as swine ulis coliform infections and pilosis passive immunization in man has been largely abandoned in favor of chemotherapy for the treatment of infections in this group in the third and important class of virus infections again the whole organism is the antigen again there is no soluble Toxin and again we must have recourse to the organisms themselves but here it is more often possible to use not inactivated killed organisms but attenuated living strains which although harmless to the host nevertheless can be used to induce fairly solid active immunity this is an important principle if a virulent organism from one species is introduced into a second species represented here by this triangular symbol the organism May develop but in so doing may change in character or become attenuated but because the attenuated organism is so closely related to the Vigilant type from which it is derived it may still possess High antigenic activity against infection by the Vigilant type so that when reintroduced back into the original species it affords protection though it is no longer fully to that species in a similar way the vaccinia virus provides protection against the closely Allied small poox virus strains attenuated by various methods are used for the preparation of vaccines for use against the number of both human and Veterinary virus diseases including yellow fever and poliomyelitis and canine distemper hard pad and rinder pest in the case of canine distemper the species used for the uation and growth of the virus is the chick embryo the living virus is inoculated into the region of the embryo of hen's eggs incubated for 8 Days a similar procedure is adopted in the case of yellow fever after a further period of 6 days incubation the virus concentration reaches its highest level in the embryo which is then removed prior to homogenizing and separation of the vaccine and filling into ampols because such vaccines are unstable in solution they are finally freeze-dried in this apparatus the dried vaccines retain their potency for some months if stored at 5° Centigrade they contain the living virus in a state of suspended animation the potency is determined by reconstituting the vaccine and estimating the virus concentration by inoculation onto the cardio allantoic membrane of embryonated eggs macroscopic lesions develop after 5 to 6 days the active immunity induced by the use of attenuated living virus vaccines is usually high in some cases however vaccines are prepared containing not living but killed viruses here for example poliomyelitis strains grown on monkey kidney tissues and inactivated by formaly are being Blended to produce a vaccine of the sulk type there are of course living attenuated vaccines available as well samples taken are tested by inoculation of monkeys the protection afforded by most killed virus vaccines is as might be expected somewhat lower than that given by living attenuated strains moreover antisera for Passive immunization against virus diseases are generally only effective if homologous in this short account we have only been able to touch upon but a few of the principles which lie behind the various methods available today for conferring immunity against both human and Veterinary infections and there is much that has been left unsaid we have for example said nothing about the use of combined prophylactics such as defia tetanus petasus vaccine or braxi black leg pulpy kidney vaccine or about the possible adant effect which one antigen May exert on another we have said nothing about the possible role of interference in virus diseases the subject is vast and its complexity as great as the complexity and multiplicity of disease itself nevertheless certain fundamental principles emerge we note that we can distinguish between two basic forms of immunity active in which the body itself is trained to produce its own protection and passive in which the body plays no direct part but in which Aid is brought in from outside we note the important principle that active immunity is in general slow to build up lasting in character and when it falls capable of Rapid restoration whilst passive immunity develops rapidly but is transient in effect and we further note that active immunity in a mother may be transferred as temporary passive immunity to newly born Offspring against diseases due to toxin producing bacteria like deia and tetanus in man and lamb dysentry and ppic kidney disease in animals we note that we can induce a high degree of active immunity by use of toxoids or their derivatives and confer useful passive protection by use of antitoxic CER against diseases caused by pathogen enic bacteria which do not produce a toxin from which we can prepare a toxoid such as hooping cough and anic fever in man and Swine Eris and poster alosis in animals we note that we can often induce useful immunity by use of killed bacterial vaccines though with the exception of some animal diseases we also note that in this class chemotherapy has now largely superseded passive immunization in treatment against virus infections such as yellow fever in man and canine temper we note that we can induce a high degree of active immunity by use of living attenuated virus vaccines and against infections such as poliomyelitis a useful degree of protection by use of killed inactivated virus vaccines we note however that passive immunity in this class is usually obtained by the use of certain homologous antisera produced from the same species these then are the fundamental principles which today form the basis of all modern immunizing procedures both human and Veterinary principles and procedures which have enabled major advances to be made in the control of disease and which together with improved methods of hygiene have reduced many one-time major scourges to negligible proportions the range of prophylactics is great and through continued research is ever becoming even greater we have indeed come a long way from Jenna who over 100 50 years ago laid the foundation of this important and evergrowing science of Immunology e