Evolution of the lymphocyte

Decreased immune response in zebra finches exposed to sublethal doses of mercury

Mercury (Hg) is a ubiquitous contaminant with deleterious effects on many wildlife species. Most studies to date have focused on fish-eating birds and mammals because much historical Hg pollution is aquatic. Recently, however, comparable blood-Hg levels have been found in terrestrial insectivorous songbirds. As a result, research is needed to clarify the effects of Hg exposure on songbirds. One fundamental end point that is still poorly understood is the effect of Hg on the songbird immune system. If Hg affects the functioning of the immune system, exposed songbirds may be less able to mount an appropriate immune response against invading pathogens. To gain insight into how Hg affects songbird immune function on a cellular level, a flow cytometric assay was developed to measure lipopolysaccharide-induced B-lymphocyte proliferation in zebra finches (Taeniopygia guttata). This is the first experimental (dosing) study of the potential effect of Hg on songbird immune system functioning. Decreased B cell proliferation was observed after lipopolysaccharide exposure in individuals with greater concentrations of Hg in their blood and tissues. In addition, these individuals had decreased ratios of proliferating-to-resting B cells. This decrease in lymphocyte proliferation in response to an effective mitogen suggests that environmental exposure to sublethal levels of Hg may inhibit or delay B cell proliferation in songbirds, potentially increasing susceptibility to disease and decreasing survivorship.

Inappropriate gene expression in human cancer and its far-reaching biological and clinical significance

This article provides a broad overview of the field of inappropriate gene expression in many organisms across the animal and plant kingdoms as well as its importance to human disease in general and cancer in particular. Study of the topic is especially important for understanding how the chaotic maelstrom of evolving and cascading regulatory genetic interactions in an advancing cancer produces its clinical effects and for designing pragmatic solutions to how such disorder might eventually be tamed. It is emphasized that the topic warrants much more attention in research and in clinical practice because of the added value it brings to refining cancer diagnosis and treatment and to the assessment of prognostic markers. It is also particularly relevant to understanding the etiology and extensive clinical manifestations of paraneoplastic syndromes affecting multiple organs remote from the tumor and the treatment or amelioration of the substantial morbidity that they cause in cancer patients. More broadly, inappropriate expression can be caused by a number of mechanisms including mutations, rearrangements of the genome, and viral insertions and, under prolonged selection pressures, also has the potential to be an agent of evolutionary change.

Invertebrate cytokines: the phylogenetic emergence of interleukin-1

Cytokines are polypeptides released by activated vertebrate blood cells which have profound effects on other blood cells and which have hormone-like properties affecting other organ systems as well. In recent years a wide variety of these mediators has been isolated and characterized. Many of these molecules have subsequently been cloned and expressed in E. coli. The tremendous importance of these proteins to host immune and non-specific defense systems along with the striking similarities of their properties among different species suggested to us that cytokines may have been proteins that have been conserved through evolution. Investigations of the evolution of cytokines will help us decipher the complex cellular, humoral and molecular interactions that regulate host defenses. Studies of the invertebrates will shed light on the phylogenetic emergence of these molecules as well.

Ontogeny of gut-associated lymphoid tissue (GALT) in the dogfish Scyliorhinus canicula L

Cartilaginous fish occupy a fundamental position in vertebrate phylogeny and it is likely that this group has retained some of the ancestral immune mechanisms. The ontogeny of GALT has received little attention in elasmobranchs and this study correlates this development with morphological differentiation, development of other lymphoid organs, exposure to seawater and transition from yolk dependence to exogenous food as a source of nutrient. GALT was first represented by individual lymphocyte-like and macrophage-like cells in the lamina propria. In later stages accumulations and intraepithelial leucocytes were recorded prior to hatching. The size of accumulations and the number of lymphocyte and macrophage-like cells infiltrating the lamina propria and epithelium increased in fish as they became dependent upon an exogenous diet. Although GALT developed after the thymus and lymphoid-like tissue in the kidney and at approximately the same time as the epigonal, Leydig and spleen, the source of cells populating the gut is unknown. Plasma cells and granulocytes were not observed in the developing fish until 6 months post-hatch after which the fish had a similar GALT distribution and content to the adult fish.

Naturally occurring agglutinins against trypanosomatid flagellates in the haemolymph of insects

In vitro studies of the behaviour of the trypanosomatid flagellates Trypanosoma brucei and Leishmania hertigi in the presence of cell-free haemolymph of locusts, Schistocerca gregaria and cockroaches, Periplaneta americana revealed the presence of parasite agglutinins. The range of normal values of agglutination titres was 2(-4) to 2(-13). Physico-chemical treatment of haemolymph indicated that these agglutinins are protein or glycoprotein in nature and are only partially affected by heat treatment below 65 degrees C, at which temperature incubation of haemolymph for 30 min abrogated all agglutination. Agglutination was not dependent on the presence of Ca2+ or Mg2+. Prior injection of locusts and cockroaches with T. brucei and L. hertigi significantly increased agglutinin titres between Days 4 and 6 in cockroaches (P less than 0.05) and from Days 2 to 4 when L. hertigi was inoculated into locusts. The induced differences in titres observed in locusts infected with T. brucei were not significant. Lysozyme levels were significantly increased after inoculation of T. brucei into cockroaches compared with placebo-inoculated and uninoculated controls. L. hertigi inoculation produced significant increases in lysozyme levels compared with controls between Days 1 and 7 in locusts and 3 to 6 in cockroaches. These studies indicate that, at least in easily manipulated model systems, induced responses to intrahaemocoelic inoculation to trypanosomes and Leishmania can occur. As far as we are aware this is the first report of an induced response of an insect to such important parasites. The possibility that induced responses in natural vector to this parasites occurs requires investigation.

Immunoglobulin-bearing blood leucocytes in the Pacific hagfish

The occurrence of immunoglobulin (Ig) bearing leucocytes in the blood of the Pacific hagfish, Eptatretus stoutii , was examined using a murine monoclonal antibody (45.3) and a rabbit antiserum specific for hagfish serum Ig. Binding of antibody 45.3 to hagfish leucocytes assessed by radioimmunoassay was inhibited by preincubation of antibody with purified serum Ig thus verifying the presence of cell surface Ig cross reactive with serum Ig. The monoclonal antibody identified approximately 65% of blood leucocytes as Ig+ve while the rabbit antiserum indicated 81% Ig+ve cells. Both antibody preparations failed to react specifically with cells from mouse, horned shark, tunicate or sea star; this indicates the distinctive nature of hagfish Ig. The high percentage of blood cells bearing surface Ig in the hagfish raises the possibility that lymphocyte divergence to separate B and T pathways may not have occurred in this most primitive vertebrate. Alternatively, an Ig-like specificity characteristic of both "T" and "B" lymphocytes may have been detected. In any event, a subset of Ig negative leucocytes is evident in hagfish.

Immune characteristics of graft rejection in nemerteans of the genus Lineus

The rejection of xenogeneic grafts in marine worms of the genus Lineus (Nemertea) gives evidence for the occurrence of immune mechanisms in these invertebrates. First, second-set response is anamnestic with a three-month memory component. Second, the accelerated rejection of second-set grafts occurs anywhere in the body of the recipient, that is to say it is systemic. Third, the anamnestic response is species-specific since it takes place only when second grafts are from donors of the same species as that of the first set. It is therefore plausible that the reaction to xenogeneic grafts is a cell-mediated immune mechanism and that the self-nonself discrimination may be a function of nemertean cells specialized for recognition at the species level and for memory.