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Searching for microbesPart VII.
Complementfixing test and neutralization
Ondřej ZahradníčekTo practical of VLLM0421c
Content of this slideshow
Dynamics of titre
Complement and its properties
Complement fixing test (CFT), its principle
Trouble shooting in CFT
Examples of CFT use in practice
Neutralization reaction – principle
Individual neutralization reactions
ASO and its importance
Dynamics of titre
Interpretation of serological reactions• Antigen detection: it is a direct
method. Positive result means presence of the microbe in the pacient‘s body
• Antibody detection: it is an indirect method. Some ways how to assess, when the microbe met the body:– Amount of antibodies (titre) and mostly
its changes during the time (dynamics)– Class of antibodies: IgM/IgG (More in J08)– (Avidity of antibodies)
Dynamics of titre• Absolute amount of antibodies is
not the most sure information: some patients are poor antibody-producers, etc.
• Dynamics of titre: better, means how the response gets changed during the time (usually during two or three weeks)
1 first pacient‘s visit
1
2 after 2 – 3 weeks
2
Why the titre alone is not sufficient
• Sometimes a patient with low reactivity has a low titre even in an accute phase
On the contrary, a very reactive patient has a high titre long after the reaction
Pair sera and non-pair sera• Pair sera = first specimen is kept in
the refrigerator until the second comes to the lab (cca 10–14 days), and thed examined together. 4-fold increase is told to be significant under such circumstances
• Other situations (second specimen is examined separately): an accidental error should be taken into account. So even 4-fold increase is not certain, it is recommended to have better proof.
Dynamics of titre – more aspects
• A special situation is so named seroconversion – there are no antibodies in the first specimen (it is too soon), but there are antibodies in the second one. Such a finding is more sure than the four-fould increase
• Sometimes titre decrease is found instead of increase (a subaccute infection)
• titre value does not correspond to infection activity. Often the highest amount of antibodies comes after the end of disease.
Examples of various effects of titre dynamics:
• 1 – 2: seroconversion• 3 – 4: titre elevation• 5 – 6: titre decrease
Complement and its properties
The Complement
• part of non-specific humoral immunity
• a complex cascade system
http://img.tfd.com/dorland/thumbs/complement.jpg
Complement-fixing test (CFT)
• Complement = one component of immunity reaction
• For CFT, we use animal (guinea-pig) complement. The patient‘s complement is inactivated before the reaction
• Complement is not able to get bound to isolated antigen
• Complement is not able to get bound to isolated antibody
• Complement is only able to get bound to the COMPLEX antigen – antibody
• When sheep RBCs are used as antigen and rabbit antibodies against them as antibody, then after binding of complement haemolysis occurs. We can see this in a simple task in the practical session.
Complement and its properties
http://web.indstate.edu/thcme/micro/comp_fix.gif
Complement fixing test (CFT), its principle
Tale 1• There was a curious park guard.• He wanted to know the true relations
between a boy and a girl that used to visit his park. Are they a couple, or they aren‘t?
• He knew, there is one only bench in the park. When one wanted to embrace somebody else somewere, one had to do it there.
• So, he placed parts of a plant (globules with hooklets, see next slide) on the bench with hope, that the couple would catch them on their clothes
The plant
http://www.ordinace.cz/clanek/lopuch-vetsi-lopuch-plstnaty/
However – how to ascertain…• …when both the girl and the boy used
another exit?• Then the guard realized, that during a
moment his niece and her boy-friend will come to him, and he was sure, that on the way through the park, they will certainly use the bench for embracing.
• And so he made a plan: when his niece and her boy-friend will have globules on them, it means, that the first couple was no true couple, as it did not catch the globules first.
What to learn from the tale• Today we have to learn complement
fixing test, quite a complicated test.• Not only that we use complement to
visualize antigen-antibody complex, but also two more parts of the reaction: the indicator couple (niece and boy-friend).
• This couple consists of indicator antigen (sheep RBC) and indicator antibody (amboceptor = rabbit antibody against sheep RBC)
CFT principle• Patient serum is mixed with
laboratory antigen (or laboratory animal serum with patients specimen in direct CFT).
• Complement is added. It binds in positive case (it is only able to bind when a complex Ag-Ig is present)
• In the 2nd phase, we add indicator system (sheep RBCs + amboceptor). In positive reaction indicator system remains intact. In negative reaction the indicator system is haemolysed
CFT – principle
Complement – how it reacts with the indicator systemThe haemolysis requires presence of sheep
(not rabbit) antibodies, amboceptor and complement. One of components missing or replaced no haemolysis.
Sheep RBC + amboceptor without complement no haemolysis
Sheep RBC + complement without amboceptor no haemolysis
Rabbit RBC + complement + amboceptor no hemolysis
Sheep RBC + complement + amboceptor haemolysis
Use of CFT
• CFT is used for diagnostics of many (mainly viral) pathogens
• CFT, like other serological reactions, may be used for antigen detection or antibody detection
• For simplification, we shall only speak about antibody detection in this practical
• So, we think about a laboratory antigen being mixed with patient‘s serum (where we search for antibodies
Trouble shooting in CFT
Problems existing in CFT
• Too much complement: false negative results. What to do? Titrate the complement to asses the proper amount
• Something in serum binding the complement itself (anticomplementarity component): false positive results. What to do? Perform anticomplementarity test – like normal course of CFT, but without antigen (A situation like a homeless man sweeping the plant globules from the bench, even when the boy did not come into the park because he was ill)
Titration of complement• For the reaction, we need an amount of
guinea-pig complement that is neither too small nor too big
• That is why we test, what amount of complement is just able to perform haemolysis of a specified amount of red blood cells with amboceptor
• Too big amount of complement false negativity (too many plant globules some of them remain for niece&boy-friend)
Anticomplementarity test
Examples of CFT use in practice
Clinical situation A• A patient with long term respiratory
problems, a few clinical signs, the most probable diagnosis: atypic pneumonia
• Atypic pneumonia may be caused by many respiratory viruses, but also several bacteria (Mycoplasma, Chlamydia)
• Eventual mycoplasmal/chlamydial etiology would mean effect of antibiotics. In viral etiology antibotics would have no effect
Respiratory pathogens• The whole seropanel belongs to one
patient.• We have six respiratory pathogens,
each in two rows (acute speciemen, reconvalescent specimen).
• First collumn = the anticomplementarity test
• Then we have seven dilutions of sera, i. e. dilution 1 : 5 in 2nd collumn, 1 : 10 in 3rd etc., with coeficient two. Besides viruses, a bacterium Mycoplasma pneumoniae is in the panel, too (difficult culture)
Clinical situation B• We have three patients with suspicion
for tick-borne encephalitis, all of them with neurologic symptoms and anamnesis of being bitten by a tick
• Tick borne encephalitis is a disease quite common in central Europe. Although it has worse course in adults (mostly seniors), people tend to vaccinate rather their childrens and not their parents.
Tick-borne encefalitis• We test antibodies again, now against
tick-borne encefalitis.– positive control in the first row– in 2nd and 3rd row the first patient– in 4th and 5th row the second patient– in 6th and 7th row the third patient
• Each patient has two rows (accute serum and the reconvalescent one)
• In the first collumn, we have anticomplementarity tests again, and then sera dilutions, starting from 1 : 4 (continued: 1 :8, 1 : 16, 1 : 32, 1 : 64 etc.)
Clinical situation C
• We have several patients that should be screened for presence of antibodies againts toxoplasmosis (Toxoplasma gondii is a tissue parasite, cat is the definitive host)
• Seronegativity means that the person never met the infection*. Seropositivity should be studied in more details (one more sampling, eventually ELISA reaction for immunoglobin class assessment)
*Or the infection is so fresh that the antibodies had no time do be created.
Toxoplasmosis• The seropanel belongs to a positive
control (1st row) and three patients (2nd to 7th row)
• We search for antibodies against toxoplasmosis.
• There are anticomplementarity tests in the first collumn, and then dilution by geometric row starting from 1 : 8.
• Each patient has only one row (we do not follow titre dynamics)
Neutralization reaction – principle
Tale 2• Once there was a killer toxin, and the toxin
wanted to kill a red blood cell• That toxin had in also character of an
antigen, that chalenges the body to produce antibodies
• And when the toxin prepared for killing the RBC, an antibody, crossed his way, bound to it and did not allow him killing
• The red blood cell was very happy, and it sedimented to the bottom with other RBCs.
What to learn from the tale• Today, we have also neutralization
reaction• This reaction is important in viruses and
bacterial toxins, that can be directly neutralized by a corresponding antibody
• The whole bacterium is rarely neutralized like that
• Majority of neutralization application is in virology. An exception is the most common serological reaction at all – ASO reaction
Neutralization reactions: general principle
• There are many ways, how antibodies do work. One of them is direct neutralizing effect
• This effect is rarely present in whole bacteria. On the other hand, it may be observed in whole viruses, and in bacterial toxins
Nevertheless, sometimes antibodies neutralize some characteristic of the whole bacteria, e. g. motility of Treponema in Nelson‘s test
Neutralization schematically• Antibody (Ig) prevents an effect of a
toxin/virus to a cell / red blood cell
Cell in a tissue culture or a red blood cell
Toxin or virus
Toxin or virus
Antibody
+ –Cell in a tissue culture or a red blood cell
Examples of neutralization reactions
Neutralized Object Reaction
Bacterial toxin (haemolysin)
RBChaemolysis
ASO
Virus RBC agglutination
HIT
Virus Cell metabolic effect
VNT
Individual neutralization reactions
ASO• Principle: The antibody blocates the
haemolytical effect of the toxin (streptolyzin O) on the RBC. Positive is blocation of haemolysis (as in CFT, but for a different reason)
• The microtitration plate is composed of a positive control and seven patient
• The titre above 250 is supposed to be risky for an autoimmune disease.
Course of serum dillution – ASO
Common course (dillution with reometric row, coefficient 2) would be too rough, we need a more detailed one. In fact, it is a geometric row too, but the coefficient is 1,2 and not two as usually
HIT• Haemagglutination Inhibition Test: Pay
attention, it is NOT an agglutination reaction, it is a neutralization! Antibody neutralizes the aggregation of RBCs due to viruses.
• So: Potato-like shape = negative response. Dense round target = positive response
• Example of use: We can read HIT results for tick-borne encephalitis. In each patient an accute and a reconvalescent serum is evaluated
Interpretation of accute vs. reconvalescent sera is of course the same as in any other serological reaction
Remember:• HIT is not an agglutination reaction,
it is neutralization of viral agglutination• HIT differs from ASO reaction mostly by
the fact, that the RBCs are not haemolyzed, but agglutination. But the fact, that a specific antibody blocates the reaction is valid in both of the
• HIT for detection of antibodies against tick borne encephalitis (unlike ASO) is again a typical „indirect diagnostic“
HIT for tick-borne encephalitis: example of a clinical situation• We have several patients with
suspicion for tick borne encephalitis, already tested using complementfixing
• Now we have decided to use an independent test to check the results
VNT (do not confuse with TNT
)
• Virus Neutralization Test• Cell culture uses to be dammaged by
a virus. The dammage is visible as a change of colour from original yellow to changed red (pH is changed)
• Antibodies, if present, may prevent this viral action on the cell culture, so the colour remains yellow
• titre = last well with unchanged colour
VNT – clinical situation• Patient R. S., 35 years, has chronical
pain in chest. Cardiological examination showed suspition for inflamation of heart muscle (myocarditis)
• As coxackieviruses are common causative agent of myocarditis, it was decided to perform test of antibodies against these viruses
VNT – example of use in coxsackieviruses
• The whole panel belongs to one patient examination. Odd rows = accute serum, even rows = reconvalescent rows. Every two rows = one coxsackievirus (B1 to B6)
• First collumn has dillution 1 : 5 (then 1 : 10, 1 : 20…)• Last collumn = controls. When there are six yellow
and six red wells here, everything is OK.• titre is the last well with unchanged (yellow)
collour.• When two coxsackieviruses have a significant (at
least four-fold) increase of titre, it might be a co-infection, but it is more likelly that the coxsackievirus with the lower titre has a cross-reaction only
ASO and its importance
What is the antistreptolyzin O and why we attempt to detect it
• After every streptococcal infection antibodies are produced, often including antibodies against streptococcal toxin – streptolysin O.
• Nevertheless, sometimes after infection the antibodies increase instead of decreasing. Antibodies are bound to some structures of the host organism (autoimmunity), so a „circulus vitiosus“ starts to run
• In such a situation, paradoxically the antibodies are worse than the pathogen that challenged the antibody response to protect us.
Remember:• ASO is not an indirect diagnostics
reaction, despite the fact that we search for antibodies. The aim is not to get a pathogen, but to assess the antibodies themselves, as they may be dangerous
• Indication for ASO examination: suspicion for so named „late sequellae“ of streptococcal infection: accute glomerulonephritis, or rheumatoid fever
Rheumatic Feverhttp://mednote.co.kr
Accute glomerulonephritis
www.ispub.com
Diffuse inflammatory cellular infiltration and mesangial hypercellularity (Hematoxylin and Eosin Staining: original magnification X 200)
Acute glomerulonephritis II
iws.ccccd.edu
ASO examination principle: haemolysis neutralization
In Czech Republic, abbreviation ASLO is used for the same thing as ASO in English
The End
http://web.uct.ac.za/depts/mmi/stannard/emimages.html
Tick borne encephalitis virus• Tick borne encephalitis often
infects children, serious symptoms are rather typical for adults. Despite that adults rarely let themselves vaccinated. In the first phase it has flu-like symptomas, in the second meningeal or cerebral symptomas. Letality of infection is 1–5 %.
• It is a typical arbovirus (=arthropode borne virus), rodents are source
• Diagnostics is mostly indirect.
More flaviviral encephalites and fevers
• Besides Central-European tick borne encephalitis we have more tick borne encephalites. Russian spring-summer encephalitis, is another subtype to the Central-European, less related is the scotish „louping ill“ and Omsk haemorrhagic fever.
• Also there exist Japanese encephalitis, transmitted by mosquitoes of genus Culex. Related is also West Nile fever, also mosquito transmitted. It is likely that is is present even in Czechia around Lanžhot
Tick – Ixodes ricinus
http://www.presse.uni-wuppertal.de/archiv/output/okt98
Virus of tick borne encephalitis
http://vietsciences.free.fr/khaocuu/nguyenlandung/virus01.htm
Toxoplasma gondii• It is a protozoon; cats are its source,
but people having dogs are in higher risk (dogs use to have cat faeces in their fur)
• Majority of infections in immunocompetent persons is asymptomatic, or only temporarily enlarged lymphonodes are observed.
• Ocular form is dangerous• Infection of foetus is dangerous,
too, especially in 1st trimester
Toxoplasma gondii
http://fullmal.hgc.jp/tg/icons/Toxo_ultrastructure.gif
Toxoplasma life cycle
Down: Toxoplasma cyst
in brain
http://web.indstate.edu/thcme/micro/parasitology
http://www.antoranz.net/CURIOSA/ZBIOR3/C0311/03-QZC08043-3_Toxoplasma.jpg
Toxoplasma gondiihttp://webdb.dmsc.moph.go.th/ifc_nih/applications/pics/Toxoplasma.jpg
http://www.smittskyddsinstitutet.se/upload/Analyser/ToxoplasmaSB.jpg
Toxoplasma – life cycle
http://www.dpd.cdc.gov/dpdx/images/ParasiteImages/S-Z/Toxoplasmosis/Toxoplasma_LifeCycle.gif
In some persons, toxoplasma retinitis may occur…
http://web.indstate.edu/thcme/micro/parasitology
Letality and mortality
• Letality is the ratio between the persons dying for the disease and the total of infected persons
• Mortality, on the other hand, is the average number of persons dying for a disease (usually counted per 100 000 inhabitants and one year)
Coxsackieviruses: survey of family Picornaviridae
• Family Picornaviridae contains mostly following viruses important for humans:
• enteroviruses, (name shows their way of transmission, but they cause infection mostly outside intestine!) further classified into– polioviruses – viruses of poliomyelitis– coxsackieviruses and echoviruses– newer enteroviruses 68, 69, 70 and 71
• rhinoviruses – viruses of common cold• virus of hepatitis A
Coxsackieviruses – more info• There exist coxsackieviruses A1–A22,
A24 and B1–B6• Diagnostic can be done by virus
isolation on newborn mice or tissue cultures
• Indirect diagnostic is difficult because of cross-reactions; nevertheless, it is used in coxsackieviruses of B group in suspicion for myocarditis
Coxsackieviruses – pathogenicity• CNS: aseptic meningitis (majority of
types)• herpangine (A types, mostly A4)• hand-foot-mouth disease (A16)• respiratory infections (all types)• myocarditis and other muscle
disease (B types)• lymphadenitis (all types)• relation of some types of diabetes
mellitus (B group)?
Check-up questions1. Why patient's own complement is not used for CFT and guinea
pig complement is used instead?2. What type of errors is caused by anticomplementarity of serum?3. What type of errors is caused by too big amounts of used
complement?4. Why 2-fold increase of titre cannot be considered significant?5. Why it is recomendable to use pair sera when using reactions like
CFT?6. What is the meaning ot the term „seroconversion“? 7. In what clinical situations ASO diagnostics is rational?8. Why it is not suitable to classify ASO as „indirect diagnostic
reaction for microbial detection“, althougth it is a method of antibody detection?
9. Some viruses are unable to agglutinate RBC – how does the fact influence HIT diagnostic?
10. Which is a Czech abbreviation for ASO?11. Why neutralisation reactions are rare in bacteriology?12. And one more