John D. Reynolds

Occurrence of Specific Antibodies of the IgA Class in the Bile of Rats

In pooled bile, obtained by cannulating the common bile duct of normal rats, the immunoglobulins were mainly of the IgA class but the total immunoglobulin concentration was 20 times less than in the b

A New Model of Sheep Ig Diversification: Shifting the Emphasis Toward Combinatorial Mechanisms and Away from Hypermutation

The current model of Ig repertoire development in sheep focuses on the rearrangement of a small number (∼20) of Vλ gene segments. It is believed that this limited combinatorial repertoire is then further diversified through postrearrangement somatic hypermutation. This process has been reported to introduce as many as 110 mutations/1000 nucleotides. In contrast, our data have that indicated somatic hypermutation may diversify the preimmune repertoire to a much lesser extent. We have identified 64 new Vλ gene segments within the rearranged Ig repertoire. As a result, many of the unique nucleotide patterns thought to be the product of somatic hypermutation are actually hard-coded within the germline. We suggest that combinatorial rearrangement makes a much larger contribution, and somatic hypermutation makes a much smaller contribution to the generation of diversity within the sheep Ig repertoire than is currently acknowledged.

The Genesis, Tutelage and Exodus of B Cells in the Ileal Peyer's Patch of Sheep

The ileal Peyers patch (PP) is a prominent lymphoid organ that extends 1-2 meters along the terminal small intestine of sheep. It is comprised of rapidly proliferating B cells that make major contributions to the animals total B cell system. The characteristics of this tissue in sheep have enabled a variety of novel approaches to studying both the B cell system and the contribution of PP to the mucosal immunity. The sheep ileal PP has characteristics that place it in a category similar to that of the thymus, bone marrow and the avian bursa of Fabricius. The ileal PP develops before birth and involutes while the sheep is still young. It produces B cells that populate the immune system but most of the large numbers of newly-formed B cells are rapidly destroyed by apoptosis. It has been concluded that this death is related to a selection event that examines each newly-formed cell. Antibody diversity in sheep is a post-rearrangement event, generated by the process of somatic hypermutation. A comparison of the lambda light chain gene from surviving and dying B cells indicates that when the PP is at its greatest size the dying cells have the characteristics of cells with high affinity receptors for a selecting ligand/antigen. It is proposed that if B cells proliferate in the continual presence of selecting ligand/antigen that the B cell receptor might develop a sufficient affinity to trigger apoptosis. This process might contribute to elimination of clones with high affinity for either self antigens or continually present environmental antigens.

Evidence for the existence of two distinct types of Peyer's patches in sheep.

Johann Peyer included a description of the Peyer’s patches (PP) in sheep as part of his monograph published in 1677 which provided the first detailed account of the “intestinal glands” that are found in all higher vertebrates. The inclusion of sheep in the list of species in which he noted PP was probably as a consequence of one of his other studies on the mechanisms of rumination. The PP in sheep have received attention periodically since that time. In 1928 Carlens published an account of the PP in domestic animals which included their distribution, ontogeny and age-related changes. We have recently reexamined these topics in the sheep and confirmed Carlens’ observations which showed that sheep PP have a number of important features (Reynolds and Morris, 1983).

Evidence of Differences Between Peyer’s Patches and Germinal Centers

Ever since the first description of Peyer’s patches (PP), which was probably by Marco Severino in his treatise on comparative anatomy published in 1645 (cited by Schmidt, 1959), there have been changing views on the function of these lymphoid tissues found along the intestinal tract. The first detailed study by Peyer (1677) led to the concept, which survived for almost 2 centuries, that PP were involved in mucous secretion. The attention of the microscopists in the second half of the 19th century, however, correctly identified PP as sites where lymphocytes are being produced. In 1851 Bruecke described the “milky white area” which was the follicle filled with lymphocytes. In 1862 His described what he called “vacuoles” in the lymph nodes which appeared to be similar to the follicles in the PP. Then in 1885 Flemming noted that these areas in the lymph nodes and the PP were both sites of high mitotic activity. He coined the term “germinal center” (GC) and correctly suggested that they are breeding sites of lymphocytes.

Emigration of newly formed lymphocytes from ileal Peyer's patches in lambs.

In lambs there is a long continuous Peyer’s patch of about 2m length at the end of the ileum. This patch has several peculiarities which are comparable to the primary lymphoid organ for B cells in chickens, the Bursa of Fabricius: it is well developed before birth (1), it is the largest lymphoid organ in lambs in the first few months of life, later it almost completely disappears, the lymphocyte production is not influenced by antigen (2), nearly all lymphoid cells in ileal Peyer’s patches are B lymphocytes (3).

Search for B cells ready to emigrate from sheep ileal Peyer’s patch

Flow cytometry was used to compare B cells in the sheep ileal PP with those in the emigrant population. The phenotype (PNAlo-slghi) of the emigrants corresponded to that of a small subpopulation of follicular B cells. We speculate that these cells may be about to emigrate having survived unknown selection events. Comparison of these cells with the major follicular population might give insight into the cause of the extensive destruction of B cells happening in the PP follicles.

Lymphatic Physiology and Secretory Immunity

The chyle-filled lacteals of the mesentery, and the various components of the gut-associated lymphoid tissue (GALT) were noted by the earliest anatomists, but their role in mucosal immunity became apparent relatively recently and is still a somewhat controversial topic. It is true, unfortunately, that even amongst mammals, differences in reproductive and digestive physiology and age-related changes in the GALT make a general understanding of the immune systems of their various mucosae particularly difficult. Therefore, it may be helpful to review briefly some of the factors which are thought to govern the behaviour of those lymphoid cells and humoral factors that are associated with immune reactions at mucous surfaces.