Evolutionary immunobiology

Cloning, characterization and ontogenetic expression profile of RAG-2 and IgM in angelfish (Pterophyllum scalare)

Early larval developmental stages of fish are highly susceptible to opportunistic pathogens until the complete maturation of the lymphoid organs. Knowledge of the expression pattern of important markers of adaptive immune system during the ontogenetic development is essential before vaccinating the fish. In the present study, Pterophyllum scalare (angelfish) was taken to explore the relative expression profile of developmental markers of adaptive immunity, recombination activating gene-2 (RAG-2) and immunoglobulin M (IgM). The fishes were bred and early developmental stages (0-45 days post-hatched) were used to assess the expression profile. The genes, RAG-2 and IgM were cloned and sequenced with the base pair lengths of 1958 bp and 225 bp respectively. The mRNA expression of RAG-2 appeared at insignificant level at the first day of hatching, but the expression was significantly increased from 24 dph (days post-hatching) onwards and reached its peak at 27 dph. The results proved that the maturation of lymphoid organs was completed at 27 dph as the respective protein is involved in the V(D)J recombination, important for the maturation of lymphoid organs. A similar trend was also observed in the mRNA transcript levels of IgM gene and a significantly high expression was detected from 27 dph onwards. The present study suggested that the suitable time for vaccination in P. scalare could be taken at 27 dph, as the maturation and development of lymphoid organs is completed thus helps in stimulating the adaptive response of immunity against any pathogen.

Evolutionary process and the ecology of human immune function

Evolutionary principles inform central design features of human immune defenses and provide key insights into this complicated host defense system. This article explores the selection pressures and adaptive responses that have elaborated the immune system over the course of evolution and discusses their implications for understanding contemporary immune development and function. Special attention is given to the challenges posed by diverse, rapidly evolving pathogens and the mammalian response to these challenges. The process of lymphocyte diversity generation and subsequent clonal selection is quintessentially Darwinian: pathogens provide selection pressure that drives differential replication of host immune cell lines, resulting in changes in genetic frequencies within an individual's population of lymphocytes. The immune system also incorporates nongenetic transgenerational processes in the transfer of antibodies from mother to offspring through the placenta and breast milk. The consequences of these observations for human development, health, and the ecology of immune function are considered throughout the life cycle. Specifically, evolutionary processes provide insight into autoimmunity, thymic function, lymphocyte development, infectious disease risk, and lactation. While much work in evolutionary medicine focuses on the discordance between evolved biology and rapidly changing cultural environments, with respect to the immune system, evolutionary processes may be most revealing when applied within individuals. Am. J. Hum. Biol. 11:705-717, 1999. Copyright 1999 Wiley-Liss, Inc.

The main protein of the aggregation factor responsible for species-specific cell adhesion in the marine sponge Microciona prolifera is highly polymorphic

Species-specific cell recognition in sponges, the oldest living metazoans, is based on a proteoglycan-like aggregation factor. We have screened individual sponge cDNA libraries, identifying multiple related forms for the aggregation factor core protein (MAFp3). Northern blots show the presence in several human tissues of transcripts strongly binding a MAFp3-specific probe. The open reading frame for MAFp3 is not interrupted in the 5' direction, revealing variable protein sequences that contain numerous introns equally spaced. We have studied tissue histocompatibility within a sponge population, finding 100% correlation between rejection behavior and the individual-specific restriction fragment length polymorphism pattern using aggregation factor-related probes. PCR amplifications with specific primers showed that at least some of the MAFp3 forms are allelic and distribute in the population used. A pronounced polymorphism is also observed when analyzing purified aggregation factor in polyacrylamide gels. Protease digestion of the polymorphic glycosaminoglycan-containing bands indicates that glycans are also responsible for the variability. The data presented reveal a high polymorphism of aggregation factor components, which matches the elevated sponge alloincompatibility, suggesting an involvement of the cell adhesion system in sponge allogeneic reactions.

Invertebrate immunity: another viewpoint

All vertebrates and invertebrates manifest self/non-self recognition. Any attempt to answer the question of adaptive significance of recognition must take into account the universality of receptor-mediated responses. These may take two forms: (1) rearranging, clonally distributed antigen-specific receptors that distinguish in the broadest sense between self and non-self, and non-self A from non-self B, latecomers on the evolutionary scene; (2) pattern recognition receptors, the earliest to evolve and still around, necessitating the requirement for induced second signals in T- and B-cell activation. Either strategy need not force upon invertebrates the organization, structure and adaptive functions of vertebrate immune systems. Thus, we can freely delve into the unique aspects of the primitive immune mechanisms of invertebrates. In contrast, using the opposite strategy which is still problematic, i.e. linking invertebrate and vertebrate defence, seems to give us an approach to universality that might eventually reveal homologous kinship.

Primitive cytokines: harbingers of vertebrate defense

The evolution of the immune system has awarded cytokines a key role as coordinators of the immune response. The exquisite action of cytokines in fine tuning and controlling the response raises the question of whether or not these molecules have been highly conserved through evolution. Gregory Beck and Gail Habicht have isolated and characterized two major cytokines, interleukin 1 and tumor necrosis factor, from invertebrates. In this article, they speculate on the possible function of these molecules and on the existence of other cytokines in invertebrates.

cDNA and amino acid sequences of rainbow trout (Oncorhynchus mykiss) lysozymes and their implications for the evolution of lysozyme and lactalbumin

The complete 129-amino-acid sequences of two rainbow trout lysozymes (I and II) isolated from kidney were established using protein chemistry microtechniques. The two sequences differ only at position 86, I having aspartic acid and II having alanine. A cDNA clone coding for rainbow trout lysozyme was isolated from a cDNA library made from liver mRNA. Sequencing of the cloned cDNA insert, which was 1 kb in length, revealed a 432-bp open reading frame encoding an amino-terminal peptide of 15 amino acids and a mature enzyme of 129 amino acids identical in sequence to II. Forms I and II from kidney and liver were also analyzed using enzymatic amplification via PCR and direct sequencing; both organs contain mRNA encoding the two lysozymes. Evolutionary trees relating DNA sequences coding for lysozymes c and alpha-lactalbumins provide evidence that the gene duplication giving rise to conventional vertebrate lysozymes c and to lactalbumin preceded the divergence of fishes and tetrapods about 400 Myr ago. Evolutionary analysis also suggests that amino acid replacements may have accumulated more slowly on the lineage leading to fish lysozyme than on those leading to mammal and bird lysozymes.