Atlantic salmon eggs favour sperm in competition that have similar major histocompatibility alleles

Polyandry and post-copulatory sexual selection provide opportunities for the evolution of female differential sperm selection. Here, we examined the influence of variation in major histocompatibility (MH) class I allelic composition upon sperm competition dynamics in Atlantic salmon. We ran in vitro fertilization competitions that mimicked the gametic microenvironment, and replicated a paired-male experimental design that allowed us to compare differences in sperm competition success among males when their sperm compete for eggs from females that were genetically either similar or dissimilar at the MH class I locus. Concurrently, we measured variation in spermatozoal traits that are known to influence relative fertilization success under these conditions. Contrary to the findings demonstrating mechanisms that promote MH complex heterozygosity, our results showed that males won significantly greater relative fertilization success when competing for eggs from genetically similar females at the MH class I. This result also showed covariation with the known influences of sperm velocity on relative fertilization success. We discuss these unexpected findings in relation to sperm-egg recognition and hybridization avoidance mechanisms based upon immunogenetic variation.

The relationship between major histocompatibility receptors and innate immunity in teleost fish

Studies of the innate immune system have recently shown that, in addition to its role in producing the primary response that slows down pathogens, it may also play an important role in initiating and directing the type of response that the adaptive immune system makes. These discoveries have shown a complex web of control containing new roles for the innate immune system in organizing responses of T-cell to antigens being presented by major histocompatibility receptors, as well as new roles for those receptors in innate immune responses. Both of these activities are managed through feedback networks involving elements of both the innate and adaptive immune system. This paper will discuss these newly discovered interactions and how they are influencing current theories regarding the initiation of adaptive immune responses. In particular, it will highlight the recent progress that is being made towards understanding these relationships in the immune systems of teleost fish.

Ig light chain variability in DNP(494)-KLH immunised sea bass (Dicentrarchus labrax L.): evidence for intra-molecular induced suppression

The coding sequence of the sea bass light chain was obtained by sequential anchored PCR on a head kidney cDNA library of a DNP(494)-KLH immunised sea bass. The cDNA sequence obtained codes for a leader peptide of 21aa and a mature IgL chain of 223aa. Both the amino acid sequence comparisons and neighbour-joining trees showed that the IgL chain of sea bass obtained is of the L1/G type. To study the variability of the light chain, additional PCRs on the cDNA library and cDNA from pooled head kidneys were performed. Multiple alignment of unique sequences (N=17) could be performed without introducing gaps, and showed extremely low variability in CDR1, and no variability in CDR2 or CDR3. A possible explanation for this low variability of the IgL1 chain might be the enhanced expression of monospecific anti-DNP antibodies. The isolation and characterisation of partial genomic and cDNA IgL sequences, which showed normal variability, corroborate this explanation.

Regulation of interleukin 1 beta RNA expression in the common carp, Cyprinus carpio L

The intron-exon organisation of the carp IL-1beta gene consists of 2455bp and comprises seven exons. Three IL-1beta RNA transcripts have been found in carp: (1) a fully spliced product; (2) exon 1-7 with introns 5 and 6; and (3) exon 1-7 with intron 5 only. The intron-containing products probably represent partially spliced transcripts. IL-1beta mRNA expression in carp was semi-quantitatively analysed by RT-PCR in multiple organs, including brain and pituitary. Constitutive expression of the IL-1beta mRNA was found in these organs with a predominant expression in the immune organs head kidney and spleen. Furthermore, a scattered distribution of IL-1beta producing cells was shown by in situ hybridisations of head kidney tissue. Administration of phorbol-myristate-acetate (PMA), lipopolysaccharide (LPS) or retinoic acid (RA), to phagocytes isolated from the head kidney, resulted in expression of IL-1beta intron-containing transcripts. Of these, only PMA and LPS were stimulators that induced the fully spliced transcript. A role for the nuclear factor (NF)-kappaB pathway in carp IL-1beta expression was shown with suppression of the LPS-induced IL-1beta expression by NF-kappaB inhibitor pyrrolidine dithiocarbamate (PDTC). Cortisol was able to inhibit in vitro constitutive expression of IL-1beta transcripts. Addition of cortisol simultaneously with LPS could not substantially inhibit transcription.

Modes of salmonid MHC class I and II evolution differ from the primate paradigm

Rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) represent two salmonid genera separated for 15--20 million years. cDNA sequences were determined for the classical MHC class I heavy chain gene UBA and the MHC class II beta-chain gene DAB from 15 rainbow and 10 brown trout. Both genes are highly polymorphic in both species and diploid in expression. The MHC class I alleles comprise several highly divergent lineages that are represented in both species and predate genera separation. The class II alleles are less divergent, highly species specific, and probably arose after genera separation. The striking difference in salmonid MHC class I and class II evolution contrasts with the situation in primates, where lineages of class II alleles have been sustained over longer periods of time relative to class I lineages. The difference may arise because salmonid MHC class I and II genes are not linked, whereas in mammals they are closely linked. A prevalent mechanism for evolving new MHC class I alleles in salmonids is recombination in intron II that shuffles alpha 1 and alpha 2 domains into different combinations.

The major histocompatibility class II alpha chain in salmonid fishes

In this study the characterisation of the Atlantic salmon (MhcSasa-DAA) and rainbow trout (MhcOnmy-DAA) class II alpha chain cDNA sequences is presented. The DAA sequences from these two salmonid species showed a high degree of similarity, although the Onmy-DAA(*)03 cDNA sequence differed in the cytoplasmic region. Interestingly, the Onmy-DAA(*)02 sequence has lost the second cysteine in the alpha-1 domain. However, another cysteine is present in this sequence 7 positions downstream of the cysteine which is substituted for a leucine. Despite a thorough search, only a single locus of expressed class II alpha chain sequences was identified in both salmonid species. Amplification by PCR and sequencing of the alpha-1 domain from genomic DNA of three Atlantic salmon, identified four different variants assumed to have derived from this single locus. Two of these variants originated from one individual and are likely functional alleles.

Molecular and functional characterization of a fish inducible-type nitric oxide synthase

Using an oligonucleotide primer based on a partial goldfish inducible nitric oxide synthase (iNOS) sequence, a complete carp iNOS cDNA was isolated from an activated carp phagocyte cDNA library. Nucleotide and predicted amino acid sequence analysis indicate that carp iNOS encodes a 1,127-amino acid protein with 57% sequence identity to human iNOS. Like mammalian NOSs, carp iNOS protein contains putative binding sites for heme, tetrahydrobiopterin, calmodulin, flavine mononucleotide, flavine adenine dinucleotide, and NADPH. Phylogenetic analysis, using neighbor joining, showed that the carp iNOS protein clustered together with the other vertebrate iNOS proteins. Inducibility of carp iNOS was confirmed by reverse transcription-polymerase chain reaction after stimulation of carp phagocytes with lipopolysaccharide or the protozoan blood flagellate Trypanoplasma borreli. These stimulators produced high amounts of nitric oxide that were toxic for T. borreli in vitro. The nuclear transcription factor NF-kappaB was shown to play a role in the induction of iNOS transcription.

Characterization of MHC class I and beta(2)-microglobulin sequences in Atlantic cod reveals an unusually high number of expressed class I genes

Degenerate polymerase chain reaction (PCR) primers based on conserved residues from alignments of species with already characterized major histocompatibility complex (MHC)-encoded sequences were used in the search for class I and beta(2)-microglobulin (b(2)m) genes in Atlantic cod (Gadus morhua L. ). After PCR amplification and subsequent sequencing a putative class I sequence was identified, from which a probe was designed and used to screen a spleen cDNA library from one single individual. The full-length clone obtained was sequenced and shown to be a classical Mhc class I-encoded sequence. It revealed the characteristic alpha1-, alpha2-, and alpha3-domains and transmembrane and cytoplasmic region, with several conserved amino acids. A PCR amplification from the alpha2-domain to the CY-region was performed on the same library, using a proof-reading enzyme. At least 11 unique additional sequences were isolated. Moreover, sequencing of the additional cDNA clones resulted in a total of 17 different Mhc class I sequences in this individual. A Southern hybridization of DNA from four different individuals using an alpha3-specific probe confirmed this large number of genes. Interestingly, based on differences mainly in their transmembrane region, the sequences obtained could be divided into two distinct groups. Within the groups no support could be obtained for any further subdivision. Southern experiments using an alpha1-specific probe gave almost the same restriction fragment length polymorphism with a high number of hybridizing bands, suggesting a low divergence in this part of the gene. Sequencing of PCR clones obtained with a proof-reading enzyme confirmed this at the nucleotide level. PCR amplification to isolate and characterize the b(2)m gene resulted in a sequence which was used to screen a thymus cDNA library. Two different alleles were obtained and these showed the characteristic features of known teleostean beta(2)m sequences. A Southern hybridization with genomic DNA from four different individuals suggested the presence of one b(2)m locus in Atlantic cod.

Identification and characterization of a fish natural resistance-associated macrophage protein (NRAMP) cDNA

The mouse Lsh/Ity/Bcg locus regulates natural resistance to intracellular pathogens, and the Nramp1 gene was isolated as its candidate. Nramp is part of a small family of at least two genes, Nramp1 and Nramp2. In the present study, a full-length cDNA for carp NRAMP has been isolated and characterized. Nucleotide and predicted amino acid sequence analysis indicate that the carp NRAMP encodes a 548 amino acid membrane protein with 12 putative transmembrane domains, two N-linked glycosylation sites, and an evolutionarily conserved consensus transport motif. The peptide sequence identity among carp and human NRAMP2 is 78%, and 65% with human NRAMP1. Reverse transcription-polymerase chain reaction revealed that carp NRAMP is ubiquitously expressed. Phylogenetic analysis, using neighbor-joining, showed that the carp NRAMP protein clustered together with mammalian NRAMP2 proteins.

A divergent non-classical class I gene conserved in salmonids

Complementary DNA for two class I genes of the rainbow trout, Oncorhynchus mykiss, were characterized. MhcOnmy-UBA*01 is similar to Onmy-UAC32 and the classical major histocompatibility complex class I genes of other fish species, whereas Onmy-UAA*01 is divergent from all class I genes so far characterized. Onmy-UAA*01 is expressed at lower levels than Onmy-UBA*01. Although Onmy-UAA*01 exhibits restriction fragment length polymorphism on Southern blotting, the encoded protein is highly conserved. Two allotypes, which differ only by substitution at amino acid position 223 of the alpha 3 domain, have been defined. Onmy-UAA*01 has an exon-intron organization like other class I genes and contains a Tc1-like transposon element in intron III. Orthologues of Onmy-UAA*01 have been characterized in four other species of salmonid. Between four species of Oncorhynchus, UAA*01 proteins differ by only 2-6 amino acids, whereas comparison of Oncorhynchus with Salmo trutta (brown trout) reveals 14-16 amino acid differences. The Onmy-UAA*01 gene has properties indicative of a particularly divergent non-classical class I gene.

Major histocompatibility genes in cyprinid fishes: theory and practice

The first teleostean MHC sequences were described for carp. Subsequent studies in a number of cyprinid fishes showed that the class I sequences of these fishes are of particular interest. Two distinct lineages (Cyca-Z and Cyca-U) are found in the common and ginbuna crucian carp, but only the U lineage is present in zebrafish and other non-cyprinid species. The presence of the Z lineage is hypothesised to be the result of an allotetraploidisation event. Both phylogenetic analyses and amino acid sequence comparisons suggest that Cyca-Z sequences are non-classical class I sequences, probably similar to CD1. The comprehensive phylogenetic analyses of these sequences revealed different phylogenetic histories of the exons encoding the extracellular domains. The MHC genes were studied in laboratory and natural models. The natural model addressed the evolution of MHC genes in a Barbus species flock. Sequence analysis of class I and class II supported the species designation of the morphotypes present in the lake, and as a consequence the trans-species hypothesis of MHC polymorphism. The laboratory model involves the generation of gynogenetic clones, which can be divergently selected for traits such as high and low antibody response. The role of MHC molecules can be investigated further by producing a panel of isogenic lines.

Expression of MhcCyca class I and class II molecules in the early life history of the common carp (Cyprinus carpio L.)

In this study transcription of class I alpha chain (Cyca-UA), beta2-microglobulin (Cyca-B2m) and class II alpha (Cyca-DXA) and beta (Cyca-DAB) during the early stages of embryo development was investigated by semiquantitative PCR. No transcripts of the genes under investigation were detected in the unfertilized egg. The expression of the genes encoding for the class II molecules revealed to be synchronized starting at day 1, unlike those for the class I molecules. Transcription of Cyca-B2m was first detected at day 7, whereas Cyca-UA was already present on day 1. This discrepancy would suggest absence of class I molecules during early development. The transcription of the Mhc genes in lymphoid organs was well established on day 21, with the exception of the spleen. In later stages of ontogeny cell surface expression of class I molecules was studied using polyclonal antibodies to Cyca-UA and Cyca-B2m in conjunction with detection of surface Ig. In week 3-10 Cyca-B2m was found on a higher percentage of cells from pronephros, spleen and thymus compared to Cyca-UA, suggesting the use of an alternative class I alpha chain. In the thymus, unlike the other organs, this difference remained present in the adult stage. The most likely candidates are alpha chains encoded by non-classical class I genes.

Expression and temperature-dependent regulation of the beta2-microglobulin (Cyca-B2m) gene in a cold-blooded vertebrate, the common carp (Cyprinus carpio L.)

Expression of beta2-microglobulin (beta2m) in the common carp was studied using a polyclonal antibody raised against a recombinant protein obtained from eukaryotic expression of the Cyca-B2m gene. Beta2m is expressed on peripheral blood Ig+ and Ig lymphocytes, but not on erythrocytes and thrombocytes. In spleen and pronephros, dull- and bright-positive populations could be identified correlating with the presence of erythrocytes, thrombocytes, and mature leucocytes or immature and mature cells from the lympho-myeloid lineage, respectively. Thymocytes were shown to be comprised of a single bright-positive population. The Cyca-B2m polyclonal antiserum was used in conjunction with a similarly produced polyclonal antiserum to an MHC class I (Cyca-UA) alpha chain to investigate the expression of class I molecules on peripheral blood leucocytes (PBL) at different permissive temperatures. At 12 degrees C, a temporary downregulation of class I molecules was demonstrated, which recovered to normal levels within 3 days. However, at 6 degrees C, a lasting absence of class I cell-surface expression was observed, which could be restored slowly by transfer to 12 degrees C. The expression of immunoglobulin molecules on B cells was unaffected by temperature changes. The absence of the class I cell-surface expression was shown to be the result of a lack of sufficient Cyca-B2m gene transcription, although Cyca-UA mRNA was present at comparable levels at all temperatures. This suggests that class I expression is regulated by a temperature-sensitive transcription of the Cyca-B2m gene.

Immunogenetics of disease resistance in fish: a comparative approach

The study of the genetic regulation of infectious disease resistance depends on the availability of inbred lines or selection lines of the species under investigation. The small numbers of such lines of fish has limited the strategy in teleosts to studies of associations between disease and immune/health traits. Attempts to correlate genetic differences in immune responsiveness with survival after experimental challenge with pathogenic bacteria have failed to define immune parameters that can substantially aid selection for genetic resistance to infectious diseases. Advantages and disadvantages of selection strategies as illustrated by mouse and chicken models are discussed. In this study we summarize the present situation in fish as well as our attempts to develop gynogenetic lines of carp for immunogenetic research.

Evidence for multiple distinct major histocompatibility complex class I lineages in teleostean fish

In the context of studies on the expression of MhcCyca-Z sequences of the common carp, PCR amplifications of exon 4 were performed on cDNA obtained from pooled thymi of 20 carp F1 individuals. Five recombinant clones (Cyca-TC3, -TC13, -TC15, -TC17 and -TC18) were found to be 96% similar to the exon 4 region of Cyca-ZA1. Each of the five sequences was unique, and differed in a few positions in both the nucleotide and the derived amino acid sequences from any of the Cyca-Z sequences known to date. These data suggest that multiple Z genes per locus are present in the carp, which are transcribed in the thymus. In the course of analysing the amplified Cyca-Z sequences, serendipity yielded a clone, Cyca-TC16, containing a class I-like sequence substantially different from any other carp class I sequence. The predicted amino acid sequence of Cyca-TC16 was most similar to the class I genes (Lach-U) from the coelacanth (42-46% amino acid identity). Cyca-TC16 contains three conserved beta 2-microglobulin contact residues, and the secondary structure was predicted by computer algorithms to be similar to that of the alpha 3 domain of HLA-A2. Phylogenetic analysis shows that carp class I sequences reside in four distinct clusters: (i) Cyca-Z, Cyca-TC3, -TC13, -TC15, -TC17 and -TC18 together with Caau-Z from ginbuna crucian carp, (ii) Cyca-U with Bree-U (zebrafish) and Sasa-p30 (Atlantic salmon), (iii) Cyca-TC16 with Lach-U (coelacanth), and (iv) Cyca-C4.

Characterization of isogenic carp (Cyprinus carpio L.) lines with a genetically determined high or low antibody production

Antibody production to dinitrophenyl-keyhole limpet haemocyanin (DNP-KLH) served as the immune parameter to divergently select carp (Cyprinus carpio L.) to produce high- and low-responder F1 hybrid lines. Antibody production to trinitrophenyl-lipopolysaccharide (TNP-LPS) and to DNP-KLH were similar in magnitude. By contrast, some high-responder lines were low responders to DNP-human serum albumin, and vice versa. Low-responder carp were relatively susceptible to infection with the parasite Trypanoplasma borreli. This suggested that at least one gene with a major influence on resistance differed between the two homozygous parents (69, 85) used to generate the high- and low-responder homozygous families, respectively. The isogenic lines showed no within-line variation in DNA fingerprints, but differed with respect to their MhcCyca-DAB genes.

Characterization of class II A and B genes in a gynogenetic carp clone

A prerequisite for carrying out functional studies on major histocompatibility complex (Mhc) molecules of fish is the availability of genetically well-defined homozygous strains. Previously we have applied gynogenetic reproduction to generate isogenic carp, denoted clone A410. This clone has recently been demonstrated to express a single class I gene, Cyca-UA1(*)01, and in the present study two class II B and two class II A transcripts were obtained. The two class II B transcripts, Cyca-D(CB3)B and Cyca-D(CB4)B, as well as the class II A transcripts, Cyca-D(10A)A and Cyca-D(15A)A, appear to be bona fide class II transcripts, based on the presence of conserved protein characteristics of the inferred class II molecules. With the isolation of class II A sequences, representatives of all major classes of Mhc genes have been identified in the carp. To assess the relationship between the different class II genes, segregation studies, comparison of cDNA and intron 1 sequence data, and phylogenetic analyses were undertaken. These showed that the class II B transcripts, Cyca-D(CB3)B and Cyca-D(CB4)B, are derived from related, closely linked loci. In addition, these studies indicated that the previously described Cyca-DAB*01 and Cyca-DAB*02 are also closely linked, but that this linked pair segregates independently from the Cyca-D(CB3)B and Cyca-D(CB4)B loci. The class II A transcripts are most likely derived from separate loci and do not represent alleles, as they were found not to segregate in the individuals of the clone which was generated by meiogenetic gynogenesis.

Identification and characterization of a new major histocompatibility complex class I gene in carp (Cyprinus carpio L.)

In this study we report the finding of three representatives of a new group of major histocompatibility complex class I sequences in carp: Cyca-12 (Cyca-UA1*01), a full-length cDNA; Cyca-SP1 (Cyca-UAW1), a polymerase chain reaction (PCR) fragment from cDNA; and Cyca-G11 (Cyca-UA1*02), a partial genomic clone. Comparison of the amino acid sequences of Cyca-12, Cyca-SP1, and Cyca-G11 with classical and non-classical class I sequences from other species shows considerable conservation in regions that have been shown to be involved in maintaining the structure and function of class I molecules. The genomic organization of Cyca-12 has been elucidated by analysis of a partial genomic clone (Cyca-G11, in combination with PCR amplifications on genomic DNA of a homozygous individual. Although the genomic organization is similar to that found in class I genes from other species, the 3' untranslated region contains an intron which is unprecedented in class I genes, and intron 2 is exceptionally large (+/-14 kilobases). Southern blot analysis indicates the presence of multiple related sequences. In phylogenetic analyses, the Cyca-UA sequences cluster with class I genes from zebrafish and Atlantic salmon, indicating that the ancestral gene arose before the salmonid/cyprinid split, approximately 120-150 million years ago. The previously reported class I Cyca-Z genes from carp and Caau-Z genes from goldfish cluster as a completely separate lineage. A polyclonal antiserum (anti-Cyca12) was raised against a recombinant fusion protein containing most of the extracellular domains of Cyca-12. The antibodies showed substantial reactivity to the recombinant protein and an Mr 45000 protein in membrane lysates of spleen and muscle, as well as to determinants present on leucocytes in fluorescence-activated cell sorter analyses. Erythrocytes and thrombocytes were found to be negative.

Detection of MHC class II transcripts in lymphoid tissues of the common carp (Cyprinus carpio L.)

In all vertebrates studied to date, the expression of MHC class II genes is known to be restricted to a limited number of tissues and cell types. In order to have a better understanding of the function of the equivalent genes in teleost fish, the distribution of MHC class II beta transcripts (Cyca-DAB) in the common carp (Cyprinus carpio L.) was investigated. RNA was isolated from tissues and leucocytes, cDNA was produced, and amplification of the Cyca-DAB genes was carried out by PCR. Of the organs with known immunological function, the highest level of Cyca-DAB transcription was found in the thymus. Despite their expected different cellular organization, total blood, head kidney, spleen and the second segment of the gut had similar Cyca-DAB expression levels. No class II transcripts were detected in the skeletal muscle. The studies carried out with leucocytes isolated from the lymphoid tissues point to a direct correlation between the levels of expression and the amounts of surface immunoglobulin positive (sIg+) cells present in the different cell fractions. However, thymus leucocytes did not follow this correlation since the highest level of class II expression was found in a thymocyte fraction that contained very low numbers of Ig+ cells. In PBL the Ig+ cells were highly positive whereas the Ig- were weakly positive. Adherent leucocytes shown to be class II positive, although adherent cells from PBL show a lower level of expression compared to those from the spleen and head kidney.

Investigations into the ubiquitous nature of high or low immune responsiveness after divergent selection for antibody production in common carp (Cyprinus carpio L.)

This paper reports on the selection of individual carp with a high or low antibody response, in combination with reproduction by gynogenesis, in order to develop well-characterised inbred carp lines consisting of practically unlimited numbers of carp with the same genotype. Two homozygous progenies, previously characterised as having a high or low immune response to dinitrophenyl keyhole limpet haemocyanin (DNP-KLH), were immunised with either a T-dependent (DNP-human serum albumin (DNP-HSA)) or T-independent (trinitrophenyl lipopolysaccharide (TNP-LPS)) hapten-carrier complex. In comparison with the antibody response after DNP-KLH immunisation, the response to DNP-HSA was observed to be highly variable and did not differ between the divergently selected progenies. This suggests that the divergent selection for antibody production to DNP-KLH has been carrier-specific. Immunisation with T-independent TNP-LPS induced a very rapid response which differed between the high and low responders, and likely measured changes in the DNP-specific precursor pool of B cells caused by the selection. A number of selected individuals with a high immune response to DNP-KLH were infected with Trypanoplasma borreli, a haemoflagellate parasite of carp, to examine a possible relationship between the increase in immune responsiveness and disease resistance, but no change could be detected. However, individual homozygous carp were able to escape inbreeding depression and survive the infection. Such carp would be likely candidates for gynogenetic reproduction to obtain viable inbred carp lines.

The production of gynogenetic Atlantic salmon, Salmo salar L

The production of Atlantic salmon gynogenomes by the combined use of a novel method for sperm irradiation and differently timed high hydrostatic pressure shocks is described. Sperm solutions were exposed to UV irradiation in a temperature-controlled flow-through device. Eggs fertilised with such sperm were exposed to shocks of 9500 psi at 30 min or approximately 7 h after fertilisation in order to produce meiotic and mitotic gynogenomes respectively. Yields of meiotic gynogenomes were generally high (up to 95%); those of mitotic gynogenomes were lower (range 2-20%). Analyses of the offspring by ploidy status and fingerprinting confirmed their gynogenetic origin. Small numbers of mitotic gynogenetic fish were grown on for 2 years in fresh and salt water. S1/S2 ratios were lower in gynogenetic fish and mean age at maturity was greater. Of the presumptive gynogenetic fish subjected to destructive sampling (n = 87) all were female.

Fish major histocompatibility complex genes: an expansion

The advent of polymerase chain reaction technology has provoked a large amount of progress in the field of fish major histocompatibility complex (MHC) research. Many new teleost sequences have been reported in the last four years, including representatives of all classes of MHC genes. While the intron-exon structure of teleost MHC genes is now becoming clear, the organisation of the genes within the teleost MHC is still unclear. The sequences reported to date have been used for phylogenetic analysis and, due to their evolutionary position, are discussed in relation to hypotheses regarding the origin of the MHC. Teleost MHC gene sequences are also examined to see if conserved features of the both the nucleotide and amino acid sequences of higher vertebrate MHC genes are present. Differences in these features will reflect functional differences between teleost and mammalian MHC genes and may also have evolutionary implications.

Divergent selection for antibody production in common carp (Cyprinus carpio L.) using gynogenesis

A base population (n = 101) of carp, consisting of a single hybrid cross, was immunized with the hapten-carrier complex DNP-KLH, to perform a divergent selection for antibody response. Measurement of the DNP-specific antibody response at 12 and 21 days postimmunization, allowed the classification of a low number of individual carp as early/high (10%) or late/low (13%) responders. Three individuals defined as early/high and three defined as late/low responding, were gynogenetically reproduced to obtain corresponding homozygous progenies within one generation only. Upon immunization with DNP-KLH, the antibody response was found to be significantly higher in the early/high responder homozygous offspring. Although the homozygosity of the offspring apparently caused a (s)lower antibody response (compared with the base population), the differences between the high and low responder offspring to indicate a genetic influence on the antibody response. The realized heritability (h2) for antibody production was estimated at 0.37 +/- 0.36. The present study provides the basis for a divergent selection of homozygous inbred carp lines with a genetically controlled difference in antibody response. These inbred lines will allow us to investigate relationship(s) between immune responsiveness and resistance to infectious diseases in fish.

Polymorphism and estimation of the number of MhcCyca class I and class II genes in laboratory strains of the common carp (Cyprinus carpio L.)

Restriction fragment length polymorphisms (RFLPs) have been identified in the Mhc of the carp (MhcCyca) using class I (Cyca-Z) and class II (Cyca-YB) specific probes. The K1-5 and K2-1 probes were obtained as PCR products after amplification of genomic DNA from a European carp using primers deduced from genomic sequences, and were shown to be 90% and 80% similar to Cyca-Z exon 3 and Cyca-YB exon 2 sequences, respectively. Six carp strains of different geographical origins and genomic status were studied. In homozygous gynogenetic carp strains the class I probe K1-5 hybridized to 9-12 fragments, whereas the class II probe K2-1 hybridized to 3-5 fragments. Thus, the Cyca consists of multiple class I and class II genes. The level of polymorphism of the Cyca genes of the strains studied was calculated as the percentage of polymorphic fragments among the total number of fragments observed, and was shown to be 70% for class I and 40-66% for class II genes. In addition, a possible correlation was investigated between a serologically defined locus K, which was demonstrated previously to incorporate class I-like characteristics, and molecular genotyping using the class I probe. Two gynogenetic families, which were serologically typed K1 and K2 homozygous, also differed in their RFLPs using a class I probe. This would suggest that the K locus is part of the Cyca complex.

Characterization of beta 2-microglobulin transcripts from two teleost species

Using degenerate primers based on published beta 2-microglobulin sequences we were able to obtain an expected 111 base pairs (bp) polymerase chain reaction (PCR) fragment from tilapia genomic DNA. The sequence of this fragment showed a high degree of similarity to mouse beta 2-microglobulin at the protein level. We used these primers in an "anchored PCR" to obtain a 213 bp PCR fragment from a carp cDNA library. This was then used to clone a full-length beta 2-microglobulin cDNA from carp. The carp sequence showed the highest similarity to rabbit beta 2-microglobulin. Both sequences showed strong similarities to all previously published vertebrate beta 2-microglobulin sequences. The predicted protein secondary structure of both the carp and tilapia clones was almost identical to the corresponding regions of previously known vertebrate beta 2-microglobulin protein sequences. When either the carp or tilapia probes were used against corresponding northern blots, they hybridized to a message of approximately 800-1000 bases long, which corresponds to the previously published lengths of beta 2-microglobulin mRNAs. Southern blotting indicated that beta 2-microglobulin was encoded by a single copy gene in both cases. Phylogenetic analysis indicated that the sequences were related to the beta 2-microglobulins of higher vertebrates but grouped together in an ancestral position.

Glomerulopathy Induced by Graft-Versus-Host Reaction in the Rat. Requirement of Donor CD4+ T Lymphocytes and MHC Class II Incompatibility at the Lymphoid Compartment

Graft-versus-host reactions (GVHR) can be associated with several autoimmune phenomena involving the kidney as a target organ. By transferring lymphocytes of AO rats into complete Freund's adjuvant-pretreated (AO x BN)F1 hybrids, a dose-dependent GVHR with glomerulopathy was experimentally induced. IgM, IgG1, and IgG2a were deposited in the mesangial area and along the glomerular basement membrane. Eluted immunoglobulins from diseased kidneys bound to normal basement membranes and especially to laminin. Anti-laminin reactivity was also present in sera from F1 recipients with GVHR. Parental CD4+ T lymphocytes were required and sufficient to induce GVHR and glomerulopathy in sublethally irradiated F1 hybrids. Using various F1 hybrids, MHC class II incompatibility was shown to be required for the induction of GVHR-associated glomerulopathy. Across MHC class I incompatibility, GVHR without glomerulopathy could be induced, provided that both CD4+ and CD8+ donor T lymphocytes were administered. Finally, MHC incompatibility between donor T lymphocytes and the recipient non-lymphoid compartment was found to be sufficient for the induction of GVHR, but not for GVHR-associated glomerulopathy. The results indicate that alloreactive donor CD4+ T lymphocytes have to interact directly with MHC class II alloantigen bearing host B lymphocytes in order to stimulate the latter to produce (auto-)antibodies. GVHR-induced glomerulopathy shares several immunopathological features with HgCl2-induced autoimmune glomerulopathy in the rat.

A major histocompatibility locus in fish: serological identification and segregation of transplantation antigens in the common carp (Cyprinus carpio L.)

In this study, experiments are described that were designed to investigate whether fish have an immune regulatory systems similar to the major histocompatibility complex (MHC) in higher vertebrate species. From combinations of gynogenetic carp showing either slow or fast rejection of skin transplants, the latter were chosen for alloantiserum production by hyperimmunization with peripheral blood leucocytes. The resulting alloantisera were analyzed for hemagglutinating reactivity with gynogenetic siblings and proved to be operationally monospecific in absorption experiments. The serologically determined carp erythrocyte specificities were shown to correspond to two codominantly expressed allelic products of a single locus and were designated K1 and K2, respectively. Flow cytometer analysis revealed that the same products are also present on leucocytes from peripheral blood, thymus, spleen, and pronephros. K1- and K2-homozygous second-generation gynogenetic siblings were used to study the histocompatibility nature of the K locus products. Skin transplants between K-allogeneic gynogenetic siblings were rejected significantly faster than within K-syngeneic combinations. Taken together, these data suggest that the K locus incorporates MHC class I-like characteristics.

Recognition of rat dendritic cells by a monoclonal antibody

A mouse monoclonal IgM antibody reactive with dendritic cells (DC) from the Brown Norway (BN) rat was prepared. This antibody (1F119) binds to a membrane-bound antigen present on DC from thoracic duct lymph, spleen, thymus, and lymph node. The antigen is present only in low density on 5% of splenic macrophages (M phi) and absent from peritoneal M luminal diameter. In situ, the antibody exhibits a strong reactivity towards DC in the thymic medulla, whereas no reaction is observed with cortical cells. Furthermore, cells positive for 1F119 can be identified in T-cell areas of spleen, lymph node, and Peyers' patches. 1F119 was genetically restricted in that a strong reactivity was found with DC from rats of the RT1n and RT1u haplotypes, an intermediate reactivity with the RT1c haplotype, only a weak reactivity with the RT1l and RT1b haplotypes, and no reactivity with the RT1a and RT1k haplotypes. The relatively weak reactivity of 1F119 with respect to the RT1l haplotype also appeared from a weak binding of 1F119 to DC from Lewis rats, as was assessed by FACS analysis. This result was comparable to the binding of OX3 (RT1.Bl and RT1.Bu) to DC from BN rats. Studies performed on thymus sections of recombinant rat strains indicate that 1F119, despite its apparent specificity for DC, reacts with a polymorphic RT1.B product.

Thymus localization of monoclonal antibodies circumventing the blood-thymus barrier

The binding in the rat thymus of mouse monoclonal antibodies which recognize determinants present on class II major histocompatibility complex antigens (HIS 19) and all T cells (HIS 17) was studied at several intervals after in vivo injection of a single dose (8 mg) of the monoclonal antibodies (MoAb). The MoAb, injected either intravenously or intraperitoneally, penetrated the thymus initially across the thymic capsule from the extravascular space. The extent to which the MoAb penetrated both cortex and medulla correlated with serum presence of the monoclonal antibody. These results suggest that the thymus cortex and medulla are permeable to MoAb present in the extravascular compartment. If this situation is a general phenomenon, which applies to circulating self non-major histocompatibility complex antigens under physiological conditions, the current dogma relating to self-tolerance needs to be reviewed.

Graft-versus-host disease in the rat: cellular changes and major histocompatibility complex antigen expression in the liver

Cellular changes in the liver were studied during an acute lethal graft-versus-host (GVH) disease in relation to the expression of major histocompatibility complex (MHC) antigens on different liver cells. Screening for MHC antigen expression revealed that control livers contained very few Ia+ cells: mainly cells in the portal tract interstitium and a small percentage of the Kupffer cells. The changes during an ongoing GVH reaction could be separated into those related to the sinusoid-associated cells, including the liver parenchyma, and those related to the portal-tract-associated cells, including periportal hepatocytes. In the sinusoids an increase in the number of Kupffer cells was seen, now all expressing Ia antigens. No damage to hepatocytes or other sinusoid-associated cells was observed. It is postulated that the increase in both number and Ia expression of the Kupffer cells is most probably due to an increased phagocytic uptake of blood-borne cellular debris and is not a result of extensive damage to hepatocytes. In the portal tracts expanding infiltrates were found composed of Ia+ T cells and macrophages (ratio 2:1). These infiltrates are probably due to a local accumulation of lymphocytes and macrophages as a result of an interaction of migrating donor-type alloreactive T cells with recipient type Ia+ cells present in the portal tract interstitium, which also interfered with normal recipient lymphocyte and macrophage traffic. Damage to portal-tract-associated cells was slight and confined to bile duct epithelial cells, which now expressed Ia antigens, and to periportal hepatocytes. In conclusion, these data do not indicate that damage to liver parenchyma plays a major role in the pathogenesis of an acute GVH reaction.

Lymphocyte migration across major histocompatibility barriers in splenectomized rats

Localisation and migration patterns of iv injected radio-labelled thoracic duct (TD) lymphocytes were studied in particular with regard to passage through lymph nodes and re-entry into thoracic duct lymph. To avoid unwanted splenic sequestration of migrating lymphocytes presenting alloantigens to the recipient, only splenectomized recipients were used. Donor cells and recipients differed at the MHC (RT-1) locus, either in fully allogeneic (AO -- greater than BN and v.v.) or semi-allogeneic (AO -- greater than AO X BN and v.v.) combinations. In two of these combinations (BN -- greater than AO and AO X BN -- greater than AO) deficient output in TD lymph correlated with deficient localisation in lymph nodes and high amounts of radioactivity in the liver. In the other allogeneic combination (AO -- greater than BN), however, high TD output (i.e. when compared with the syngeneic combination BN -- greater than BN) correlated with good localisation in lymph nodes and low (control) levels of radioactivity in the liver. It was postulated that lymphocyte migration from blood to lymph under these circumstances can only be studied as an artifact secondary to whether or not migrating cells are removed from the circulation before they can reach and cross HEV's. These Allogeneic (or Altered) Lymphocytes Removing Tissues (by definition: Extranodular) may (conceptually) be comprised within one system: ALERT. It is our working hypothesis that the study of lymphocyte migration across (major) histocompatibility barriers is seriously impaired by the functioning of ALERT. It might be worthwhile to try and create conditions in which interference by this system is prevented, e.g. by using tolerant animals or bone-marrow chimeras.