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

The immune response of carp to Trypanoplasma borreli: kinetics of immune gene expression and polyclonal lymphocyte activation

Although Trypanoplasma borreli induces the production of non-specific antibodies, survival of infection is associated with the production of T. borreli specific antibodies, able to lyse this parasite in the presence of complement. During the lag phase of this acquired immune response, innate immune mechanisms must limit multiplication of T. borreli. A heat-labile fraction of T. borreli together with CpG motifs in the DNA of this parasite are responsible for the induction of nitric oxide (NO) and probably also for the induction of expression of the inflammatory cytokines tumor necrosis factor (TNF)alpha and interleukin (IL)-1beta by carp phagocytes in vitro. In the signal transduction pathway leading to activation of phagocytes, protein tyrosine kinase and protein kinase C are involved and probably collaborate in activation of the transcription factor nuclear factor (NF)-kappaB. In vivo, carp intraperitoneally injected with T. borreli up-regulate expression of TNFalpha, IL-1beta and mRNAs for acute phase response proteins (complement factor 3, serum amyloid A and alpha-2-macroglobulin).

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.

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.

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.

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.

Genetic variation in susceptibility to Trypanoplasma borreli infection in common carp (Cyprinus carpio L.)

Gynogenetic reproduction of homozygous females, or crossbreeding two homozygous animals, results in fish lines without genetic variation. Hybrid crosses are expected to express a more stable development than homozygous lines, the latter may have an important value for gaining insight into genetic components of host resistance to parasite infection. We examined the antibody response of carp (Cyprinus carpio L.) to infection with Trypanoplasma borreli. Outbred carp responded with a production of specific antibodies, but highly susceptible isogenic hybrid carp did not. This suggests an apparent relationship between susceptibility and the lack of specific antibody production. This relation was partially confirmed by the passive transfer of immunity with immune plasma. In addition, two isogenic homozygous carp lines were highly susceptible to the trypanoplasm (100% mortality), in contrast with outbred carp, the majority of which survived infection. None of the carp in either homozygous carp line produced an antibody response to parasite-unrelated antigen (DNP-KLH). This suggests that the low antibody response was not entirely due to a poor state of health, but that these carp have a genetically predetermined low antibody response.