Immunology 1977 32 373

Biological properties of goat immunoglobulins G

V. V. MICUSAN & A. G. BORDUAS Centre de Recherche en Immunologie,Institut Armand-Frappier, Ville de Laval, Quebec, Canada

Received 22 December 1975; acceptedfor publication 22 June 1976

Summary. The serum concentration of normal adultgoat total IgG was established to be 19 97 ±155mg/ml, the IgG1 10 92±0 84 mg/ml and IgG2907±078 mg/ml. No significant variations werefound to be associated with the seasons of the yearbut changes in concentration, especially in serumIgG1 occur ante- and post-partum. In goatcolostrum, the IgG concentration is about 2 4-2-8times greater than in serum and the IgG1 subclassaccounts for 95-98 per cent. During the immuneresponse the IgG1 rises sharply whereas variationsin IgG2 concentration are less evident. Both IgGsubclasses are active in haemagglutination, althoughthe IgG1 is 22-52 times more efficient. As in allruminants, only IgG1 fixes complement in theclassical test. Differences exist between IgG sub-classes in their ability to induce PCA reactions.IgG2 subclass is active only in homologous specieswhereas the IgG1 in heterologous species. Cyto-philic activity is associated with IgG2 subclass.

INTRODUCTION

In the last decade progress has been made in theisolation and characterization of domesticatedbovidae immunoglobulins. These studies haveshown that bovine (Butler, 1969; Mach & Pahud,

Correspondence: Dr V. V. Micusan, Laboratoire d'Im-munochimie, Centre de Recherche en Immunologie, InstitutArmand-Frappier, C.P. 100, Ville de Laval, P. Qu6., CanadaH7N 4Z3.

1971; Butler & Maxwell, 1972a; Butler, Maxwell,Pierce, Hylton, Asofsky & Kiddy, 1972b; Duncan,Wilkie, Hiestand & Winter, 1972; Vukotic, 1972;Lisowski, Janusz, Tyran, Morawiecki, Golab &Bialkowska, 1975b), ovine (Aalund, Osebold &Murphy, 1965; Harrison & Mage, 1967; Heimer,Clark & Maurer, 1969; Sullivan, Prendergast,Antunes, Silverstein & Tomasi Jr., 1969; Lisowski etal., 1975b) and caprine (Gray, Mickelson & Crim,1969; Givol & Hurwitz, 1969; Strausbauch, Hurwitz& Givol, 1971; Micusan & Borduas, 1974; Micusanand Borduas, 1975a) immunoglobulins have thegeneral features of those from other mammals as wellas particular properties. Three classes of immuno-globulins i.e. IgM, IgA and IgG have been recognizedin the above mentioned species. A secretorycomponent attached to IgA has also been identifiedand isolated (Mach, Pahud & Isliker, 1969; Pahud &Mach, 1970; Butler, 1971).The IgG class of all bovidae is composed of two

subclasses, IgGI and IgG2 which differ in theirphysico-chemical and biological properties. A fourthclass of immunoglobulins having similar propertiesto the human IgE has been identified in bovine(Hammer, Kickhofen & Schmid, 1971; Wells &Eyre, 1972a, b), ovine (Hogarth-Scott, 1969) andcaprine species (Micusan, V.V. unpublished results).More immunochemical and biological characteriza-tion is needed in order to confirm the existence of thisclass in bovidae.

Despite the great number of publications onphysico-chemical properties of bovidae immuno-

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V. V. Micusan & A. G. Borduas

globulins, less information is available on theirbiological properties. Because of the wide-spreaduse of commercial goat IgG antisera, we havestudied the biological properties of IgG1 and IgG2subclasses in this species. We have investigated theirconcentration in normal blood serum, in colostrum,during immunization together with their complementactivation, skin fixation and reaction with macro-phages.

MATERIALS AND METHODS

AnimalsIn all experiments goats of mixed breed were used.They were clinically healthy during the entireexperiment.

Preparation of IgG1 and IgG2 from goat serum andcolostrumSerum IgG1 and IgG2 were isolated according tothe method described by Gray et al. (1969), withsome modifications. These consisted mainly of arechromatography of each immunoglobulin sub-class on CM-cellulose (Whatman CM-52) using0-01 M phosphate, pH 7-5 as starting buffer followedby an up to 04 M NaCl gradient.

Colostral IgG was obtained from colostral wheywhich was prepared by centrifugation and caseinprecipitation according to the method describedby Aalund (1968). IgGi and IgG2 subclasses wereisolated by column chromatography on DEAE-Sephadex A-50 as described in the legend of Fig. 3.When necessary, IgG 1 and IgG2 fractions werepooled, concentrated and rechromatographed onSephadex G-200.IgG1 and IgG2 preparations contained no other

proteins as determined by immunodiffusion andimmunoelectrophoresis using antisera to wholegoat serum or goat colostral whey.

Quantitative determination of immunoglobulinsThe concentrations of IgGi and IgG2 were deter-mined by automated immuno-precipitin reactions(AIR) using the fluoronephelometer TechniconAuto-Analyser II. Guinea-pig antisera againsttotal immunoglobulins, against total IgG and againstIgGl were used to develop the immune reactions.These antisera have been manually prediluted withsaline to a previously determined working con-

centration (1/25 for the anti-IgG serum; 1/30 for theanti-IgGI serum). Throughout the experiments asample line delivering 0-1 ml/min and an antiserumline delivering 0-32 ml/min were used. The samplerate was 50/h. The nephelometer was working withhighest sensitivity. Standard curves with purifiedIgG and IgGI were used for calculations. Theconcentration of IgG2 was calculated by differencebetween the concentration of the total IgG and thatof IgGl. Before testing, Na2 EDTA (7 mg/ml) wasadded to each serum sample to avoid complementcoprecipitation. By this method reproducible resultswere obtained to within ± 10 per cent in samplescontaining between 2-15 mg immunoglobulin/mland ± 20 per cent with samples of lower con-centrations. Serum and colostrum samples contain-ing more than 15 mg immunoglobulin/ml werediluted accordingly.

Immunization ofgoatsFour adult goats aged from 10-21 years wereinoculated subcutaneously with 2 mg of humangamma globulin (HGG) in Freund's completeadjuvant (FCA). The animals were injected again4 weeks later with the same preparation. Twogoats were injected i.v. with 30 mg of killed andlyophilized Calmete-Guerin bacilli (BCG). Thesecond administration of antigen took place 4 weekslater after a previous desensitization.

Isolation ofpurified antibodiesAnti-HGG antibodies were isolated with an im-munoadsorbent formed of HGG and bovine serumalbumin cross linked with glutaraldehyde (Avrameas& Ternynck, 1969). After intensive washing the anti-HGG antibodies were eluted from the immuno-adsorbent with 0-1 M glycine-HCl buffer pH 2-8 andimmediately adjusted to pH 7 6. The IgGl and IgG2antibodies were separated by chromatography onDEAE-Sephadex A-50.

Quantitative determination of anti-HGG and anti-BCG antibodiesSpecific antibodies to HGG were measured by usingthe method described by Antoine & Avrameas(1973). Briefly, an appropriate volume of anti-HGGserum was mixed with a constant volume of dis-persed immunoadsorbent. The mixture was stirredgently for 30 min at room temperature and thencentrifuged. The precipitate was suspended andwashed several times in phosphate-buffered saline

374

Biological properties ofgoat IgG

until the absorbance at 280 nm of the washing fluidswas less than 0 05. The antibodies were eluted with0-1 N HCO and the concentration was determined bymeasuring the absorbance (A 'l"' = 13 8 at 280 nm).The recovery of the control samples ranged from96-105 per cent. The anti-BCG antibodies weredetermined by the AIR method using an antiserumagainst total goat immunoglobulins. The valueswere obtained by difference between the non-absorbed goat antisera and that of the same anti-sera absorbed with BCG.

Guinea-pig antiseraGuinea pigs were immunized against total goatimmunoglobulins (1gM, IgA, IgG), goat IgG(IgGI and IgG2) and goat IgG1 after the methoddescribed by Binaghi, Oriol & Boussac-Aron (1967).The anti-IgG1 was rendered subclass specific byrepeated absorption with purified IgG2 obtained as

previously described.

ImmunoelectrophoresisImmunoelectrophoresis was performed as describedby Scheidegger (1955). Precipitin lines were devel-oped with guinea-pig anti-goat serum or colostrum.

Passive haemagglutination and passive haemolysisHaemagglutination and haemolysis tests were

performed using sheep red blood cells tanned andsensitized with HGG according to Boyden's method(1951). Guinea-pig serum previously absorbed withsheep red cells was used as the source of complementfor haemolytic tests.

Complement fixationThe test was performed according to the micro-method described by Casey (1965) using 5CHsoguinea-pig complement units. Antigen concentrationbefore serial dilutions was 1 mg/mi.

Passive cutaneous anaphylaxis (PCA)Heterologous reactions. Normal female guinea-

pigs weighing 250 g were used for PCA tests. Theanimals were injected i.d. with different concentra-tions of anti-HGG (IgG1 and IgG2 fractions) involumes of 01 ml. Four hours later, the animalswere challenged with 1 mg of HGG in 0-15 M NaClcontaining Evans blue 0 5 per cent (0-24 ml solutionper 100 g of body weight).Homologous reactions. These were performed in 3-

month-old goats. Intradermal injections of 0-1 ml

of anti-HCG (IgGI and IgG2 fractions) werefollowed by the administration of 3 mg HGG in15 ml of Evans blue 0 5 per cent in 0-15 M NaCl.Saline was used as controls.

Reverse passive Arthus reactions. Normal femaleguinea-pigs weighing 250 g were injected i.v. with1 mg HGG as described for PCA reactions andimmediately thereafter different concentrations ofanti-HGG (IgGI and IgG2 fractions) were injectedi.d. The reactions were examined 4 h later.

Reactions with macrophages. Goat white cellswere obtained from the buffy-coat of heparinizedvenous blood after centrifugation. The cells werewashed with saline and resuspended in Hanks'ssolution to a white cell count of 10,000-15,000/mm3.Normal goat IgGI and IgG2 were coupled to goaterythrocytes using chromic chloride. IgGI or IgG2in a concentration of 4 mg/ml in phosphate-bufferedsaline (PBS) was mixed with equal volumes of 0-005M CrCI3 6H20. To these mixtures goat erythrocyteswashed three times in saline were added immediately(0 25 ml of packed erythrocytes for 2 ml of mixture)and stirred gently for 5 min at room temperature.Finally the cells were centrifuged and washed fourtimes in saline and resuspended in PBS as 1 percent suspension. The presence of the cytophilicactivity was tested by rosette formation after themethod described by Abramson, LoBuglio, Jandl& Cotran (1970).

RESULTS

Concentration of total IgG, IgG1 and IgG2 immuno-globulins in adult serum and colostral wheyThe concentration of goat serum immunoglobulinswas determined monthly during 1 year, in normalgoats, six non-pregnant females and two males(Table 1). The data obtained show individual varia-tions but, on an average, the concentration of totalIgG is 1997+±155 mg/ml. The concentration ofthe IgG1 subclass represents 55 per cent of the totalIgG immunoglobulins.Changes in the serum concentrations of total IgG

immunoglobulins associated with parallel changes inIgG1 immunoglobulin were observed in pregnantanimals before and after parturition. Fig. 1 showsthe results obtained in six pregnant goats. Startingwith the 8th week before parturition we observed

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V. V. Micusan & A. G. Borduas

Table 1. Concentration of goat total IgG, IgGl and IgG2 inserum and colostrum

Animals Total IgG IgG1 IgG2

Serum A*t 19 83+ 1-25 10 80+0 69 9 10+0 74B 18-31+ 0-63 10 09+ 0-36 8-21+ 0-36C 21 03+ 090 11-39+ 056 964+ 0-46D 18 02+0 60 9 91+0 38 8-11+0-27E 20-89+ 1-02 11-42+ 0-63 9 47+ 0-48F 19-03+ 0-94 10 37+ 050 8-66+ 0-51GI 21-66+ 0-76 11-87+ 0-38 9-79+ 0-49H 20-97+ 0 85 11-47+ 0-42 9 50+ 0 57

General mean 19-97+ 1-55 10-92+0-84 9 07+0-78ColostrumT 5327+ 530 5083+495 2-27+ 132

Values presented for serum are means of 12 monthly sam-ples.

* Values expressed as mg/ml+ s.d.A-F Normal adult female goats.I G and H Normal adult male goats.T Mean of six animals on two successive lactations.

an important rise in total IgG concentration which,on an average, increased by more than 7 mg/mlover the normal level. This high level which startedto drop sharply about 4 weeks ante-partum, reacheda concentration about normal at parturition and thenrose again during the next 4 weeks.The IgG1 subclass closely paralleled the changes

observed with total IgG immunoglobulins. TheIgG2 subclass concentration, as it was calculatedby difference, varied little during the pre-partumperiod but showed a tendency to increase in thepostpartum period.

Goat colostral whey contained about 24-2-8

261-

22

18

0% 14

10

6

2l dI

2 4 6Weeks

8 10 12

E ~ ~ ~ ~ F,

6

2_

8 7 6 5 4 3 2 P 1 2 3 4Weeks

Figure 1. Changes in the mean weekly concentration ofserum total IgG ( ) and IgG (-.-.- ) before andafter parturition. Values obtained from six animals. Verticalbars indicate s.d. P = parturition.

Figure 2. Variation of serum IgG2 (- ..... V, L...E)and IgG l ( .- - - -, a - - - --. ) in the course ofimmunization of goats with HGG (-, 0) and BCG (Li, 0).Solid columns represent concentration of total anti-HGGantibody; open columns total anti-BCG antibody. The valuesare mean of four goats immunized with HGG and two goatsimmunized with BCG.

times more IgG immunoglobulins than normal goatserum. Meanwhile, the IgG1 subclass representedover 95-98 per cent of the total IgG immuno-globulins (Table 1).

Variations of goat IgGI and IgG2 immunoglobulinsduring the immune responseConcentrations of IgGI and IgG2 subclasses weredetermined during the immune response of four

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Biological properties ofgoat IgG

goats injected s.c. with HGG in FCA and of twogoats injected i.v. with killed BCG (Fig. 2). It wasobserved for both antigens that the IgG1 subclassincreased more rapidly than the IgG2 after thefirst injection of antigen. The concentration curves

showed that after reaching a peak value 3 weekslater, the amount of IgG1 dropped and this was

more evident with the response to the HGG antigen.Following the second injection of antigen theconcentration of IgG1 rose in both cases attaininghigher values than after the first injection and peakvalues were measured 3-4 weeks later. The IgG2concentration curves obtained for HGG and BCGshowed a different pattern. In the case of HGG, theconcentration of IgG2 rose slowly a week after thesecond injection of antigen and then dropped. TheIgG2 concentration curve for BCG showed no

modification except for a small increase a monthafter the second injection of BCG.The concentration of the total anti-HGG anti-

bodies rose after each antigen injection and a peakvalue was obtained a month after the second injec-tion. The total anti-BCG antibodies showed a smallincrease after the first injection of BCG which rose

after the second injection attaining a peak value 6weeks later. At the end of the experiment, it was

noticed that when the total antibody concentrationdecreased, both the IgGI and IgG2 subclasses had a

tendency to increase.

Haemagglutination, haemolysis and complementfixation of goat IgG immunoglobulins

When a purified IgG fraction from anti-HGG goatserum (pool of four animals) was chromatographedon DEAE-Sephadex A-50, two peaks were obtained(Fig. 3). The first peak eluted with the equilibrationbuffer contained the IgG2 subclass whereas thesecond, which was obtained after the NaCl gradientwas applied, contained the IgG1 subclass. Althougha small contamination of IgG2 in the second peakmay have occurred, the immunoelectrophoresis ofpooled and concentrated immunoglobulins revealedno contamination when developed with guinea-piganti-goat serum. Passive hemagglutination activitywith HGG coated sheep red cells was found in bothpeaks.However, the haemagglutinating efficiency in

the IgG1 subclass was different from IgG2. When2 + agglutination was taken for end-point, theminimal amount of IgG1 and IgG2 antibodies

90

c00

120 200

12

10 'cm

8 CP-J

6-

4-

2-

E

400 8

300

200

100

Tube number

Figure 3. (a) Immunoelectrophoresis pattern; (b) elutionprofile (0 ..... 0) of purified goat anti-HGG antibodieson DEAE-Sephadex A-50. Equilibration of the column andthe elution of first peak (IgG2) was made with 0 05 Mphosphate buffer, pH 7-6. A gradient (G . ) up to0-3 M NaCl in the same buffer lead to the elution of thesecond peak (IgG1). Haemagglutination (solid columns)and haemolysis (open columns) titres are expressed as log2.

required to produce it varied substantially. TheIgGI subclass was 22-52 times more efficient inhaemagglutination than was the IgG2.When tested for passive haemolysis in the presence

of guinea-pig complement it was observed that theIgG2 subclass was practically inactive whereashigh titres were recorded in the IgGI elution region(Fig. 3).

Table 2. Complement fixation test with guinea-pigcomplement (5 CH50 u)

Samples* CH50 (reciprocal titre)

IgG2 <4IgG2 (colostrum) <4IgG 1 256IgGI (colostrum) 128IgG total (serum) 192IgG total (colostrum) 128Normal goat serum <8

* All immunoglobulin samples contained equalamount of antibody. -

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V. V. Micusan & A. G. Borduas

Table 3. PCA and reverse Arthus reactions with IgG 1 and IgG2

Reactions TreatmentFractions Antibody

(pg) PCA Reverse Arthus 2-ME 560

I h 2h 6h

Homologous50 -

IgGI 100 - - - - -200 - - - _ _50 + + + +

IgG2 100 ++ ++ ++ ++ +200 +++ +++ +++ +++ +

Heterologous50 + +

IgGI 100 ++ ++200 +++ +++50 - -

IgG2 100 - -200 - -

The complement fixation test with pooled andconcentrated IgG1 and IgG2 fractions togetherwith fractions isolated from colostrum of the samegoats definitely confirmed that in this classicaltest and in the presence of guinea-pig complementonly the IgG1 subclass is active (Table 2).

Anaphylactic activity of goat IgG1 and IgG2 immuno-globulinsThe ability of IgGI and IgG2 to induce homologousand heterologous PCA was investigated with variousanti-HCG concentrations. The results showed thathomologous PCA was obtained only with IgG2.Heating of i.d. injected IgG2 at 560 for 6 h causeda strong reduction of the PCA activity whereastreatment of IgG2 with 2-mercaptoethanol (0-1 M)followed by iodoacetamide alkylation had no sucheffect. On the contrary, the IgG1 subclass waseffective in inducing both heterologous PCA(guinea-pig) and reverse passive Arthus reactions(Table 3).

Cytophilic activity of goat IgG2 and IgG1 immuno-globulinsThe presence of cytophilic activity of goat IgG2and IgG1 was tested by rosette formation. It wasobserved that goat macrophage and polymorpho-nuclear white cells formed rosettes, in a proportion

Figure 4. (a) Macrophages and polymorphonuclear cellsforming rosettes with IgG2 coated goat erythrocytes. (b)No rosettes are formed with IgG1 coated goat erythrocytes.

of 87-5 per cent only with IgG2 coated erythrocytes(Fig. 4a). No rosette formation occurred withIgG1-coated erythrocytes (Fig. 4b). Control forspontaneous rosettes using human albumin-coatederythrocytes was negative. Pretreatment of whitecells with IgG2 practically inhibited rosetteformation with IgG2-coated erythrocytes whereaspretreatment with IgG1 did not.

DISCUSSION

The concentration of immunoglobulins in severalbody fluids is regulated, in part, by the constant

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Biological properties ofgoat IgG

region of their heavy chains. Therefore, researchon concentration variation of immunoglobulinscan reflect some of their biological properties. Since,from all ruminant immunoglobulins, the IgG classis quantitatively the most important, we focusedour work on it. The total IgG class in normaladult goats varies around 20 mg/ml which represents18-20 per cent of total serum proteins. In normaladult animals no significant seasonable changecan be revealed except for modifications in IgGconcentration occurring in pregnancy. Early ob-servations (Popovici & Micusan, 1963) showedchanges in goat serum gammaglobulins before andafter parturition. The present study on the IgGsubclasses confirms our previous results. The riseof total IgG before parturition is the results of anincrease in IgG1 synthesis rather than an accumula-tion, since this subclass is more rapidly catabolizedthan IgG2. The phenomenon of IgGl increase isin relation with the fact that this subclass is selectivelytransported to precolostral and colostral milk ofruminants. In bovine colostrum, IgG1 accounts formore than 75 per cent of the total immunoglobulinswhereas IgG2 is present in only 5-6 per cent. Goatcolostrum is particular in this respect because theIgG1 subclass represents almost the totality of theIgG class. The mechanism of the selective transportof IgGi from blood into colostrum is still poorlyunderstood. In a previous work we showed that theFc portion of IgG1 is involved in this transport(Micusan & Borduas, 1975b).During immunization of goats with either a

soluble (HGG) or particulate (BCG) antigen itwas observed that the concentration curves of theIgG subclasses follow a different pathway. The IgG1concentrations rose markedly after each antigeninjection whereas those for IgG2 showed littlemodification. Our results are similar to the observa-tions made by Movsesijan, Jovanovic, Aalund &Nansen (1975) in their work on the immune responseof sheep to Fasciola hepatica infection. The authorsreported that IgG2 concentrations did not changesignificantly during the experimental infection,whereas the serum IgG1 concentration increased.Margni, Castrelos & Paz (1973) showed thatspecific IgG1 antibody concentrations directed eitheragainst dinitrophenyl group or against the carriermolecule, are higher than the concentrations ofIgG2. The same situation was also reported to occurin guinea-pigs (Binaghi, 1966) and mice (Barth,McLaughlin & Fahey, 1965), but other biological

properties of the IgG1 subclass in the above speciesare different from those of ruminants.The concentration of total anti-HGG or anti-BCG

antibody showed an increase after each antigeninjection. A relatively high level of antibody wasmaintained 6-8 weeks after the last injection. Whenthe total antibody concentration decreased, theIgG1 and IgG2 started to increase. This non-specific rise of IgG subclasses was also observedduring the immune response of sheep (Margniet al., 1973), guinea-pigs (Binaghi, 1966) and mice(Barth, et al., 1965) upon injection of antigen asso-ciated with FCA, as in our case.

In our experiment, as demonstrated by haem-agglutination, antibody activity was found in bothIgG subclasses, although IgGI was 22-52 times moreefficient than IgG2. This variation in haemagglu-tination efficiency found in different fractions ofIgG1 after DEAE-Sephadex chromatography re-vealed that this subclass is heterogenous. Never-theless, some contamination of IgG1 with IgG2may have occurred, at least in the ascending partof the IgGI peak which could have been responsiblefor the variations in haemagglutination efficiency.Different haemagglutinating efficiencies were alsoobserved with ovine IgG1 and IgG2 antibodies(Kaplan & Freeman, 1971) and with electrophoretic-ally slower and faster rabbit IgG (Benedict, 1965).

Haemolysis and complement fixation revealedthat only the IgG1 subclass was active. The samesubclass induced PCA and passive Arthus reactionsin heterologous species whereas the IgG2 lackedhaemolytic and complement fixation ability butinduced homologous PCA. These facts are con-sistent with the data reported for ovine IgG byFeinstein & Hobart (1969), Rhee, Broad & Jonas(1970) and Esteves, Sant'Anna, Dos Santos Annes& Binaghi (1974). It is interesting to compare theabove biological activities of the IgG of ruminantswith those found in rodents. In mice (Nussenzweig,Merryman & Benacerraf, 1964) and guinea-pigs(Ovary, Benacerraf & Bloch, 1963) homologousPCA activity was found in the fast electrophoreticIgG (IgGI) fraction whereas complement fixingactivity in its classical way was related with slowelectrophoretic IgG (IgG2).Although cytophilic activity was reported for

human and rodent immunoglobulins no such pro-perty was described for ruminant IgG. Our resultswith goat IgG showed that the cytophilic activityis a characteristic of the IgG2 subclass. On the

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380 V. V. Micusan & A. G. Borduas

Table 4. Biological properties of goat IgG2 and IgG1 immunoglobulins

Characteristics IgG2 IgG I

Complement fixation (classic) - +Concentration in serum (adult) 9-07+ 0-78 10-92+ 0-84Concentration in colostrum 2-27+ 0-32 50 83+ 495Cytophilic activity + -

Haemagglutination + +(More efficient)

Half-life (days)* 15 5-30 5 9.5- 165Homologous PCA + -

Heterologous PCA - +Immune response + +

(Most important)Passive reverse Arthus reactionPlacental transfer - +

* Data from Aalund (1968).

other hand, guinea-pig and mouse IgG2 were shownto have the property of binding to macrophageswhereas IgG1 had not (Berken & Benacerraf, 1966;Spiegelberg, 1974). In man only IgG1 and IgG3were found to bind strongly to the monocytereceptors (Huber & Fudenberg, 1968). The role ofthese cytophilic antibodies is not well understoodbut they could endow the macrophage cells withproperties implicated in macrophage-mediated im-munity.The biological properties of goat IgG are sum-

marized in Table 4. It remains, however, to furtherinvestigate other properties and thoroughly studythe mechanisms by which IgGI and IgG2 subclassesas well as other ruminant immunoglobulins areinvolved in the immune response.

ACKNOWLEDGMENTS

The authors gratefully acknowledge the skilledtechnical assistance of Mr R. Jolicoeur. We are alsograteful to Dr P. J. Neveu for helping to performskin-binding tests.

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