Antibody repertoire development in fetal and neonatal piglets. I. Four VH genes account for 80 percent of VH usage during 84 days of fetal life

VDJ rearrangement and VH gene usage during fetal development in 35 outbred piglets was examined by PCR amplification of VDJs; VDJs were subsequently characterized by hybridization with VH-specific gene probes and by sequencing. VDJ rearrangement was first seen in the fetal liver on day 30 of a 114-day gestation. Four VH genes (V(H)A, V(H)B, V(H)C, and V(H)E) accounted for approximately 80% of all VH gene usage regardless of gestational age, choice of piglet, or lymphoid tissue tested; D(H)A and D(H)B were used in >90% of the fetal VDJs examined. Evidence of somatic hypermutation during fetal development was not found. The proportion of the four prominent fetal VH genes did not differ significantly between cDNA and DNA, suggesting the absence of selective B cell differentiation. A comparison of recombination signal sequences, flanking sequences, and framework sequences of these fetal genes with other germline VH genes of swine offered no clue as to their selective usage. N-region additions were prominent on day 40 but not on day 30, suggesting that the onset of terminal deoxynucleotidyltransferase activity occurs after 30 days of fetal development. These collective findings indicate that the preimmune, "natural Ab" repertoire of the fetal piglet is largely restricted to the use of four nonpolymorphic and nonmutated VH genes and two nonmutated DH segments. This suggests that the preimmune repertoire of swine is either highly restricted or almost entirely determined by junctional diversity in complementarity-determining region-3.

Antibody Repertoire Development in Fetal and Neonatal Piglets. I. Four VH Genes Account for 80 Percent of VH Usage During 84 Days of Fetal Life

VDJ rearrangement and VH gene usage during fetal development in 35 outbred piglets was examined by PCR amplification of VDJs; VDJs were subsequently characterized by hybridization with VH-specific gene probes and by sequencing. VDJ rearrangement was first seen in the fetal liver on day 30 of a 114-day gestation. Four VH genes (VHA, VHB, VHC, and VHE) accounted for ~80% of all VH gene usage regardless of gestational age, choice of piglet, or lymphoid tissue tested; DHA and DHB were used in >90% of the fetal VDJs examined. Evidence of somatic hypermutation during fetal development was not found. The proportion of the four prominent fetal VH genes did not differ significantly between cDNA and DNA, suggesting the absence of selective B cell differentiation. A comparison of recombination signal sequences, flanking sequences, and framework sequences of these fetal genes with other germline VH genes of swine offered no clue as to their selective usage. N-region additions were prominent on day 40 but not on day 30, suggesting that the onset of terminal deoxynucleotidyltransferase activity occurs after 30 days of fetal development. These collective findings indicate that the preimmune, “natural Ab” repertoire of the fetal piglet is largely restricted to the use of four nonpolymorphic and nonmutated VH genes and two nonmutated DH segments. This suggests that the preimmune repertoire of swine is either highly restricted or almost entirely determined by junctional diversity in complementarity-determining region-3.

Human respiratory muscles: sensations, reflexes and fatiguability

1. Given the importance of the ventilatory 'pump' muscles, it would not be surprising if they were endowed with both sensory and motor specializations. The present review focuses on some unexpected properties of the respiratory muscle system in human subjects. 2. Although changes in blood gas tension were long held not to influence sensation directly, studies in subjects who are completely paralysed show that increases in arterial CO2 levels elicit strong sensations of respiratory discomfort. 3. Stretch reflexes in human limb muscles contain a monosynaptic spinal excitation and a long-latency excitation. However, inspiratory muscles show an initial inhibition when tested with brief airway occlusions during inspiration. This inhibition does not depend critically on input from pulmonary or upper airway receptors. 4. Human inspiratory muscles (including the diaphragm) have been considered to fatigue during inspiratory resistive loading. However, recent studies using phrenic nerve stimulation to test the force produced by the diaphragm show that carbon dioxide retention (hypoventilation) and voluntary cessation of loading occur before the muscles become overtly fatigued.

Absence of viscerosomatic inhibition with injections of lobeline designed to activate human pulmonary C fibres

1. Activation of pulmonary C fibres (J receptors) in animals produces inhibition of spinal motoneurones. Intravenous bolus injections of lobeline are believed to activate pulmonary C fibres (J receptors) in human subjects and to produce characteristic sensations and cardiorespiratory responses. This study quantified the respiratory sensations evoked by such injections and then used a range of suprathreshold doses of lobeline and tested for the presence of reflex or descending inhibition of motoneuronal output. 2. Injections of lobeline produced dose-dependent sensations of respiratory discomfort referred to the throat and upper chest beginning within about 10 s and often associated with coughing. As the dose increased the latency for the sensations decreased while their duration and intensity increased. Reflex changes in blood pressure, heart rate and ventilation also occurred. 3. Injections of lobeline at doses sufficient to evoke respiratory discomfort lasting 25-32 s (37-73 microgram kg-1) increased the size of the H reflex in soleus with an onset latency of about 10 s and lasting about 20 s. 4. The size of EMG responses evoked in upper limb muscles by transcranial magnetic stimulation of the motor cortex increased shortly after injections and remained elevated for about 30-35 s. 5. Injections of lobeline during sustained voluntary contractions of the elbow flexors at submaximal or maximal levels did not impair the ability to produce force. 6. Walking was not disrupted by repeated suprathreshold doses of lobeline. 7. It is concluded that injections of lobeline sufficient to evoke cardiorespiratory reflexes and sensations of severe respiratory discomfort are not associated with functionally important inhibition of motor performance. The results cast doubt on the ability of the J reflex to limit exercise in humans.

Identification, characterization and expression of Toxocara canis nematode polyprotein allergen TBA-1

We have cloned the cDNA of TBA-1, the Nematode polyprotein allergen (NPA) of Toxocara canis and found it to be most similar to ABA-1, the Ascaris NPA, on the basis of amino acid sequence. We could study the antigenic properties of an E-coli synthesized fusion protein prepared with the cloned gene since no glycosylation site was expected from the deduced amino acid sequence. Although no IgE responses to TBA-1 were detected, recombinant TBA-1 was differently recognized by serum IgG antibodies when the recombinant TBA-1 was directly adsorbed vs when immobilized via a streptavidin linkage on polystyrene microtitre wells. One group of sera recognized TBA-1 directly immobilized while the second only recognized TBA-1 immobilized via streptavidin linkage. The former were from rodents immunized with a Toxocara sp. adult worm extract while the latter were obtained from rodents infected with T. canis larva or immunized with a Anisakis simplex L3 larval extract. These observations suggest that the two in vivo forms of TBA-1 are expressed, but during different stages of the parasite's life cycle.

Determination of gene usage by differential polymerase chain reaction product hybridization

All swine VH genes belong to a highly homologous family and have identical leader sequences, and the swine VH locus contains a single JH. The small number of VH genes used by the fetus and neonate in the first 6 weeks have unique CDR1 and CDR2 sequences, permitting each to be identified using specific oligonucleotide probes. We have used this system as a model for the development of a rapid method for determining the proportional usage of closely related genes based on differential polymerase chain reaction (PCR) product hybridization (DPPH). The validity of the method is demonstrated using mixtures of PCR product containing known amounts of VH gene DNAs and by comparing data obtained by this method with those obtained by enumeration of individual hybridizing clones from lymphoid tissue and peripheral blood B cells. Since DPPH is at least 100-fold more efficient than the enumeration of individual hybridizing clones, it is especially useful for analyzing large numbers of samples in population studies. The possible extension of this method to the usage of other genes is discussed.

Immunoglobulin diversity, B-cell and antibody repertoire development in large farm animals

The B-cell lineage, the antibodies produced by these cells and the diversification of the antibody repertoire are essential for the health and survival of all mammals. Cattle, sheep, swine and horses, unlike rodents and primates, develop their antibody repertoire from a relatively small number of VH (variable heavy) genes of one or several families and cattle, sheep and horses use almost exclusively lambda-light chains. These large farm animals appear to use templated mutation (gene conversion) in addition to untemplated (point) mutation in repertoire development; this may occur predominantly in the ileal Peyer's patches. Whether B-cell lymphogenesis is continuous throughout life--as in rodents and primates--or whether B cells are largely of the B-1 lineage and develop only in foetal and neonatal life, is uncertain. The fact that immunoglobulin D (IgD) is totally absent from swine and ruminants may be significant, as IgD is expressed weakly on rodent B-1 cells. Information on IgG subclass diversity in large farm animals is incomplete, except for sheep and cattle, and no information is available for any large farm animal to show whether T helper 1 (Th1) and Th2 responses correlate with the expression of any subclass antibody response, as is the case in rodents. All large farm animals exclusively use the mammary gland to transfer immunity to offspring, although the receptor involved in the transport of IgG into colostrum and milk has not been characterised. Efforts to standardise the nomenclature and measurements of antibodies and immunoglobulins in large farm animals are discussed, and a proposal currently under review concerning the standardisation of the nomenclature for bovine immunoglobulins is presented as a model.

Contraction of the human diaphragm during rapid postural adjustments

1. The response of the diaphragm to the postural perturbation produced by rapid flexion of the shoulder to a visual stimulus was evaluated in standing subjects. Gastric, oesophageal and transdiaphragmatic pressures were measured together with intramuscular and oesophageal recordings of electromyographic activity (EMG) in the diaphragm. To assess the mechanics of contraction of the diaphragm, dynamic changes in the length of the diaphragm were measured with ultrasonography. 2. With rapid flexion of the shoulder in response to a visual stimulus, EMG activity in the costal and crural diaphragm occurred about 20 ms prior to the onset of deltoid EMG. This anticipatory contraction occurred irrespective of the phase of respiration in which arm movement began. The onset of diaphragm EMG coincided with that of transversus abdominis. 3. Gastric and transdiaphragmatic pressures increased in association with the rapid arm flexion by 13.8 +/- 1.9 (mean +/- S.E.M.) and 13.5 +/- 1.8 cmH2O, respectively. The increases occurred 49 +/- 4 ms after the onset of diaphragm EMG, but preceded the onset of movement of the limb by 63 +/- 7 ms. 4. Ultrasonographic measurements revealed that the costal diaphragm shortened and then lengthened progressively during the increase in transdiaphragmatic pressure. 5. This study provides definitive evidence that the human diaphragm is involved in the control of postural stability during sudden voluntary movement of the limbs.

Effect of contraction strength on responses in biceps brachii and adductor pollicis to transcranial magnetic stimulation

The sizes of the motor-evoked potentials (MEPs) and the durations of the silent periods after transcranial magnetic stimulation were examined in biceps brachii, brachioradialis and adductor pollicis in human subjects. Stimuli of a wide range of intensities were given during voluntary contractions producing 0-75% of maximal force (maximal voluntary contraction, MVC). In adductor pollicis, MEPs increased in size with stimulus intensity and with weak voluntary contractions (5% MVC), but did not grow larger with stronger contractions. In the elbow flexors, MEPs grew little with stimulus intensity, but increased in size with contractions of up to 50% of maximal. In contrast, the duration of the silent period showed similar changes in the three muscles. In each muscle it increased with stimulus intensity but was unaffected by changes in contraction strength. Comparison of the responses evoked in biceps brachii by focal stimulation over the contralateral motor cortex with those evoked by stimulation with a round magnetic coil over the vertex suggests an excitatory contribution from the ipsilateral cortex during strong voluntary contractions.

Sequence analysis of pig switch mu, C mu, and C mu m

The complete sequence of pig switch mu (S mu) and the various domains of C mu, a total of ca 8 kilobases (kb) of sequence, are presented and comparatively analyzed. S mu starts about 2.5 kb downstream of the single pig JH gene and ends 0.4 kb upstream of C mu; the length of S mu is 3.2 kb. Three major pentameric repeats, gagct, gggct, and gggtt, comprise more than half of the entire S mu sequence. The two most frequent decamers are gagctgagct and gagctgggct. The longest single repeated sequence is 93 base pairs. The frequency of the various pentamers indicates that pig S mu is more similar to human S mu than to mouse S mu. The sequence of genomic pig C mu and its deduced amino acid sequence are similar to the C mu sequences published for other vertebrates and are most similar to those of sheep, another artiodactyl. The membrane and secreted tailpiece exons are highly conserved (ca > 90% similarity) and are actually identical to those of the sheep. The degree of similarity to other mammalian IgMs generally decreases from the carboxyl to the amino terminal domains, with the exception of C mu 2, which shows the lowest similarity among species (61% DNA, 44% aa). As in human C mu, we identified five potential N-linked glycosylation sites, two cysteines involved in forming interchain disulfide bonds, and the two additional cysteines involved in the linkage of IgM pentamers. This is only the third species for which a S mu sequence has been reported but the first from a species lacking the second virgin B-cell receptor, i.e., IgD. IgD in mice and humans lacks a switch region and its expression depends on the splicing of C mu-bearing mRNA with C delta. However, we found no evidence that the lack of C delta influenced the genomic structure of S mu, C mu, or C mu m.

Genetic association between parameters of inmate immunity and measures of mastitis in periparturient Holstein cattle

Relationships between genetic measures of mastitis (somatic cell score, score for clinical mastitis, and scores for IMI with major or minor pathogens) and immunological parameters (physiological and molecular markers) were examined for periparturient Holstein cows. Physiological markers included 11 in vitro immunological assays. Molecular markers included the second exon of the DRB3 locus of the bovine major histocompatibility complex, the IgG2 isotype genotype, and the CD18 genotype (the locus responsible for bovine leukocyte adhesion deficiency). A gene substitution model was used to estimate the additive genetic effects of alleles of the three molecular markers on estimated breeding value (EBV) for mastitis measures. Pearson correlation coefficients between EBV for immunological assays and EBV for mastitis measures were computed. Molecular markers explained up to 40% of the variation in EBV for measures of mastitis. The presence of allele DRB3.2*16 was associated with higher EBV for SCS. Allele DRB3.2*8 was associated with increased EBV for clinical mastitis, as was the IgG2b allele and the normal CD18 allele. Alleles DRB3.2*11, *23, IgG2a, and the recessive allele for bovine leukocyte adhesion deficiency were associated with decreased clinical mastitis. A positive genetic association was found between allele DRB3.2*24 and EBV for IMI by major pathogens and between DRB3.2*3 and IMI by minor pathogens. Several correlations between EBV for immunological assays and EBV for mastitis measures were significantly different from 0. Cows with low EBV for SCS tended to have neutrophils that had greater functional ability at maximal immunosuppression, low serum IgG1, and high numbers of circulating mononuclear cells. Immunological parameters, including physiological and molecular markers, are useful aids to understand the genetics of resistance to mastitis.

Bovine IgG2a antibodies to Haemophilus somnus and allotype expression

Bovine IgG2a has been implicated in protection against pyogenic infections, including those caused by Haemophilus somnus. To further investigate the role of IgG2a in defense against H. somnus, IgG1 and IgG2a antibodies were purified from antiserum against an immunodominant 40 kDa outer membrane protein (p40) of H. somnus, which was previously shown to passively protect calves against H. somnus pneumonia. The passive protective capacity of anti-p40 IgG1 or IgG2a was evaluated in vivo in calves. Purified anti-p40 IgG1 or IgG2a was incubated with H. somnus for 15 min before intrabronchial inoculation of calves. Bacteria incubated with anti-p40 IgG1 or IgG2a were inoculated into one caudal lung lobe and bacteria incubated with IgG1 or IgG2a from the respective preimmunization serum were inoculated into the contralateral lobe. The volumes of pneumonia in the right and left lungs were determined 24 h later. The difference in volume of pneumonia with H. somnus preincubated in IgG1 pre- and postimmunization anti p40 was less (16 cm3, P = 0.298) than the difference in volume of pneumonia with H. somnus preincubated in IgG2a pre- and postimmunization anti p40 (30 cm3, P = 0.146). Although the differences in lesion size between pre- and postimmunization serum were not statistically significant, the trend suggests IgG2a may be more protective than IgG1. To examine this further, the peptide specificity of these IgG1 and IgG2a antibodies to p40 was examined. After limited proteolysis of p40, IgG2a antibodies reacted with 2 peptides not recognized by IgG1 antibodies. Other peptides were recognized by both isotypes. Since these studies suggested that IgG2a may be important in protection against infection, we then investigated some aspects of the role of the 2 IgG2a allotypes, A1 and A2. In retrospective studies of age differences in expression of IgG2a allotypes, no heterozygotes were detected in calves of 60 d old or less, and fewer heterozygotes were detected in calves 61-120 d old than in cattle older than 270 d (P < 0.01). In a subsequent prospective study of the time course of allotype expression, Holstein calves shown to be heterozygotes expressed the IgG2aA1 allotype early but the IgG2aA2 allotype was not usually detected until 3 to 4 mo of age. Thus, both the retrospective and the prospective studies showed age related differences in expression of the IgG2aA1 and A2 allotypes. This could have implication in protection.

Pulmonary afferents are not necessary for the reflex inhibition of human inspiratory muscles produced by airway occlusion

In contrast to limb muscles, the usual response of human inspiratory muscles to sudden loading consists of an initial marked reduction of electromyographic activity (EMG) followed by a subsequent increase in EMG. To determine definitively whether pulmonary receptors are necessary for this short-latency reflex inhibition produced by airway occlusion, we studied five subjects with complete pulmonary denervation due to bilateral transplantation of the lungs and five matched control subjects. Subjects with pulmonary denervation were studied between 10 and 50 days after transplantation (median 21 days). Brief airway occlusion during inspiration (i.e., loading; duration 250 ms) produced short-latency reduction in EMG in the inspiratory muscles of all subjects with acute pulmonary denervation (scalenes and parasternal intercostal muscles; mean onset of inhibition 27 and 29 ms, respectively). The ongoing EMG was reduced by an average of 50% in scalenes and 36% in parasternal intercostal muscles. The size and the magnitude of the initial response did not differ significantly from those in control subjects. After the occlusion (i.e., unloading), activity of the inspiratory muscles was transiently reduced in control subjects and patients after bilateral lung transplantation. Given that the initial responses to airway loading and unloading were preserved after bilateral lung transplantation, we conclude that these reflex responses are not critically dependent on the discharge of intrapulmonary receptors. The results support the view that the short-latency inspiratory responses to loading and unloading can be mediated by inspiratory muscle afferents. They suggest a functionally different organization of the reflex pathways for inspiratory compared with limb muscles.

Task failure with lack of diaphragm fatigue during inspiratory resistive loading in human subjects

Task failure during inspiratory resistive loading is thought to be accompanied by substantial peripheral fatigue of the inspiratory muscles. Six healthy subjects performed eight resistive breathing trials with loads of 35, 50, 75 and 90% of maximal inspiratory pressure (MIP) with and without supplemental oxygen. MIP measured before, after, and at every minute during the trial increased slightly during the trials, even when corrected for lung volume (e.g., for 24 trials breathing air, 12.5% increase, P < 0.05). In some trials, task failure occurred before 20 min (end point of trial), and in these trials there was an increase in end-tidal PCO2 (P < 0.01), despite the absence of peripheral muscle fatigue. In four subjects (6 trials with task failure), there was no decline in twitch amplitude with bilateral phrenic stimulation or in voluntary activation of the diaphragm, even though end-tidal PCO2 rose by 1.6 +/- 0.9%. These results suggest that hypoventilation, CO2 retention, and ultimate task failure during resistive breathing are not simply dependent on impaired force-generating capacity of the diaphragm or impaired voluntary activation of the diaphragm.

Characterization of the bovine C alpha gene

The complete genomic sequence of a bovine C alpha gene is reported here. The genomic sequence was obtained from a C alpha phage clone that had been cloned from a genomic EMBL4 phage vector library. The C alpha sequence had previously been expressed as a chimeric antibody and identified as IgA using IgA-specific antibodies. Intron/exon boundaries were determined by comparison of the genomic sequence with an expressed bovine C alpha sequence obtained from spleen by reverse transcription-polymerase chain reaction (RT-PCR). Analysis of 50 Swedish bovine genomic DNA samples using genomic blots and five different restriction enzymes failed to detect evidence of polymorphism. However, PstI digests of Brown Swiss DNA showed a restriction fragment length polymorphism (RFLP), suggesting that at least two allelic variants of bovine IgA exist. Comparison of the deduced amino acid sequence of bovine IgA with sequences available for other species indicated that the highest homology was with that of swine, another artiodactyl. This was the highest homology observed for all mammalian IgA compared except for that between IgA1 and IgA2 in humans. Bovine IgA shares with rabbit IgA3 and IgA4, an additional N-linked glycosylation site at position 282. However, the collective data indicate that cattle are like swine and rodents and unlike rabbits in having a single locus of the gene encoding IgA of this species.

Immunoglobulin gene organization and the mechanism of repertoire development

Recombinant DNA technology has made it possible to comparatively examine the immunoglobulin (Ig) gene constitution of numerous species. These studies reveal that many species diverge from the pattern seen in rodents and primates while revealing a number of interesting correlations involving Ig gene organization, B-cell lymphogenesis and the mechanism of repertoire development; many of these fail to correlate with traditional phylogenetic relationships. These correlates pose new questions regarding repertoire developments, which suggest that considerable diversity exists in the process. These findings also allow new questions to emerge regarding the role of IgD, the size of the B-cell repertoire, and the role that antigen may or may not play in repertoire development. These issues are discussed with the intention of stimulating experimentation to test a number of speculative hypotheses regarding B-cell and repertoire development.

Adsorption-induced antigenic changes and their significance in ELISA and immunological disorders

The functional properties of 125I-labeled antibodies and antigens adsorbed on polystyrene and silicone were compared to their counterparts immobilized by non-adsorptive methods. Less than 20% of polyclonal (pAb) and 1-2% of monoclonal (mAb) capture antibody equivalents remained functional after adsorption as a monolayer. Survivability circa doubled or was totally rescued, when the same antibodies were immobilized via a streptavidin bridge or by using a first stage polyclonal antiglobulin capture antibody, respectively. Similarly, the antigenicity of bovine IgGs for pAb and mAb anti-IgGs was highest when the IgGs were immobilized via a streptavidin bridge or when secondarily adsorbed to an albumin monolayer. IgGs in these configurations were significantly more antigenic than when directly adsorbed on polystyrene or a silicone elastomer. Similar activity was seen after adsorption on polystyrene or silicone. Interestingly, these IgGs were equally antigenic when denatured and subsequently adsorbed in 6M guanidine-HCl versus adsorption in PBS without prior denaturation. Although many of the above finding on antibodies and antigens could be explained by the greater accessibility of antigenic epitopes or antibody binding sites when molecules are immobilized by some type of underlying molecular layer, we also show that certain mAb and pAbs preferentially recognized allotopes on IgG2a when IgG2a was adsorbed. Furthermore, such antigenicity was highest when IgG2a was adsorbed at low, sub-monolayer concentrations. Finally, we show that differences in antigenicity need not be related to the method of immobilization, but can also result from differences in the microenvironment of the epitope. This was demonstrated using a filamentous phage clone specific for fluorescein (FLU). This clone recognizes the fluorescein hapten differently depending on the carrier protein used and the method of conjugation. Data presented in this report indicate that antibodies and antigens adsorbed on hydrophobic polymers undergo changes in their functional properties. Data suggest that both changes in conformation and the accessibility of antigen epitopes or antibody binding sites, most likely occur. Especially in the case of the latter, the functional concentration may be 1-2 orders of magnitude lower than the antibody protein concentration. These observations have implications for immunodiagnostics and emphasize the need to determine the specificity of an antibody in the assay in which it is employed and to make no assumptions about the behavior of solid-phase antigens and antibodies from their behavior in solution. Our studies are also relevant to the use of silicone medical prostheses. The antigenicity of IgGs adsorbed on silicone as a multilayer (secondary layer) is much higher than when directly adsorbed. Since such surfaces would be exposed to very high protein concentrations in vivo, multilayers not a monolayer, would be expected. Thus it would seem from these studies that host protein adsorbed on silicone would be expressed to the immune system at the surface of multilayers. This being the case, it seems unlikely that the adsorption of host protein in vivo would generate new epitopes against which the host's immune system could respond and subsequently initiate an autoimmune syndrome.

Comparative studies on the interaction of proteins with a polydimethylsiloxane elastomer. II. The comparative antigenicity of primary and secondarily adsorbed IgG1 and IgG2a and their non-adsorbed counterparts

The antigenicity of bovine IgG1 and IgG2a adsorbed on a polydimethysiloxane (PEP) elastomer, on a widely used polystyrene (Imm 2, Dynatech) or immobilized as biotinylated proteins to streptavidin covalently bound to polystyrene (SA-PS) was compared using various monoclonal (mAbs) and polyclonal antibodies (pAb) to bovine IgG. The IgGs were either adsorbed as native proteins or pre-denatured with 6M Guanidine-HCl (Gu-HCl) or 6 M Gu-HCl/0.1% 2-mercaptoethanol. In special situations, bovine and human IgG was immobilized by secondary adsorption to an albumin monolayer adsorbed on either PEP or Imm 2. Results indicate that pre-denaturation of IgGs with 6 M Gu-HCl/2-mercaptoethanol destroys all antigenicity whereas those IgGs pretreated with 6 M-GuHCl are indistinguishable in their antigenicity from the IgGs adsorbed to either PEP or Imm 2 without such treatment. When immobilized on SA-PS, Gu-HCl-treated IgGs were significantly less detectable, especially when tested using mAbs. In general, IgGs adsorbed on PEP or Imm 2 were less antigenic than when immobilized on SA-PS. However, two monoclonals specific for the IgG2a(A2) allotypic variant, favored the adsorbed protein and one polyclonal best recognized the IgG2a(A1) variant adsorbed on Imm 2 rather than when adsorbed on PEP or immobilized on SA-PS. Both IgG1 and IgG2a, bound by apparent protein-protein interactions to an albumin monolayer, were significantly more detectable than when directly adsorbed on either Imm 2 or PEP. Using 125I-antibody or its Fab fragment to reduce steric hindrance in detection, we observed the same differences in detectability as when measured by enzyme-linked immunosorbent assay. Failure to identify a steric hindrance effect and the preference of some antibodies for adsorbed allotypic variants, support the concept of adsorption-induced conformational change (AICC). We conclude that proteins adsorbed as a monolayer on the PEP elastomer used to form the envelope of silicone breast implants are conformationally altered, but not necessarily to the same extent or the same manner as when adsorbed on polystyrene. The significantly great antigenicity of secondarily adsorbed IgG suggests that it may be present in near native conformation.

Comparative studies on the interaction of proteins with a polydimethylsiloxane elastomer. I. Monolayer protein capture capacity (PCC) as a function of protein pl, buffer pH and buffer ionic strength

Polydimethylsiloxane (PEP) is widely used in medical prostheses and therefore is in contact with plasma and secretory proteins. Two pair of globular proteins, lactoferrin (Lf) and transferrin (Trf), and bovine IgG1 and IgG2a, which differ substantially between pair members in their pl, were used to study the interaction of a PEP widely used in breast implants and soluble protein. Studies were done using iodinated proteins over a concentration range that resulted in an apparent protein monolayer. Secondary incubations with dilute protein solutions were needed to form the monolayer on PEP, possibly as a consequence of micro air bubbles trapped on its highly textured surface as shown by atomic force microscopy. Immunoassay quality polystyrene microtiter wells were used as controls. Adsorption studies were routinely performed at pH 4, 7 and 10 and at ionic strengths corresponding to 0.95, 9.5 and 90.0 mS. The protein capture capacity (PCC) of PEP for Lf and Trf was optimal at physiological pH and ionic strength and comparable under these conditions to that of Immulon 2 (Imm 2) microtiter wells. While increasing the ionic strength and pH further increases the PCC of Imm 2 for Lf and Trf, this markedly lowered the PCC of PEP for these proteins suggesting that initial polar interactions may precede subsequent hydrophobic bonding to PEP. This was tested using a hydrophilic variant of PEP, which when tested in a 90.0 mS buffer, showed a > five-fold lower PCC at neutral and alkaline pH. The greatly reduced PCC of the hydrophilic variant might also suggest that hydrophilic variants of silicone would be more biocompatible than those currently used. The PCC of PEP for the IgGs was less than that of Imm 2 but still optimal at physiological conditions. Consistent with the data on Lf/Trf, PCC progressively decreased with increasing ionic strength at alkaline pH. Differences in pl between the protein pairs had only a marginal effect on the PCC of PEP. Monolayer adsorption on both PEP and Imm 2 was slowly reversible and greater in the presence of free ligand (< 2% in 16 h) suggesting that the process follows Mass Law principles. However, even in the presence of non-ionic detergent and free ligand, 85-90% remained bound on either surface. Thus, desorption of proteins in the monolayer should not complicate subsequent immunochemical studies conducted on adsorbed monolayers.

Polymorphism of the IGHG3 gene in cattle

We cloned and analyzed the gene (IGHG3) encoding cattle IgG3 using a spleen cDNA library and a genomic phage clone. IGHG3 differs most remarkably from IGHG1 and IGHG2 in the structure of its hinge. The IGHG3 hinge is encoded by two exons, one of which encodes a 22 amino acid 3' extension of the CH1 exon. The IGHG3 gene is highly homologous to the C-gamma pseudogene previously reported. Seventy-one DNA samples from different cattle were tested by pulsed-field gel electrophoresis and Southern blot to detect genetic polymorphisms. This analysis revealed two different alleles which we designated IGHG3(a) and IGHG3(b). The two putative alleles differ from each other by a 6 amino acid substitution in the coding region and an 84 base pair insertion in the intron between the CH2 and CH3 exons. Our data also indicate that the cattle heavy chain locus spans approximately 400 kilobases from IGHM to IGHA and encodes only three IgG subclasses, all of which are transcriptionally active.

The swine Ig heavy chain locus has a single JH and no identifiable IgD

Sequence analysis of 84 V region cDNAs expressed with IgM, IgG and IgA from both adult and newborn swine suggested that their JH segments had been derived from the same germline JH. Only a single hybridizing JH segment could be identified in genomic DNA, in a JH-C mu cosmid and in a Sacl fragment of the cosmid extending 5 kb 5' of the EnhH. The single germline JH segment mapped 6 kb 5' to C mu. This JH had a sequence identical to 40 of 42 JH segments expressed in a newborn piglet and 25 of 42 expressed by adult swine. None of the 19 JH segments which varied from the germline sequence were identical to each other and half of the nucleotide changes were silent. No cosmid DNA hybridizing with heterologous probes for C delta could be found within 20 kb 3' of C mu and C delta could not be cloned from genomic or cDNA libraries. A conserved IgD fragment could be amplified from human, mouse and rat genomic DNA but not from rabbit, swine or cattle. We hypothesize that heavy chain organization and constituency in homeothermic vertebrates is correlated with the site of secondary antibody repertoire development and the mechanism(s) used.

The VH and CH immunoglobulin genes of swine: implications for repertoire development

Swine have the largest number of IgG subclass genes of all species so far studied but have a single gene for IgA which occurs in two allelic forms that differ in hinge length. Swine also have constant region genes for C mu and C epsilon, but lack a gene homologous to that which encodes IgD in rodents and primates, despite the otherwise high degree of sequence similarity of all other swine CH genes with those of humans. Swine have < 20 VH genes, a single JH and perhaps a limited number of DH segments. Newborn piglets show preferential VH and DH usage and may use gene conversion as a mechanism for expanding their antibody repertoire. Despite the close similarity of their Ig gene sequences to humans, swine belong to the group of animals that includes rabbits, chickens and cattle when classified on the basis of B cell development. This group, unlike rodents and humans, have a single VH family, use hindgut follicles early in life (rather than bone marrow throughout life) to diversify their antibody repertoire and probably all use gene conversion. It is proposed that IgD may serve a function in repertoire development in rodents and humans which is unnecessary in the chicken-lagomorph-artiodactyl group. The diversity of immunoglobulins and immunoglobulin genes among species justifies the quest of veterinary immunologists to define the system for their species of interest rather than making extrapolations from mouse and human immune systems.