This article is concerned with the use of viral models for the study of the mechanism of protein biosynthesis and its regulation. The scope is restricted mainly to general aspects of animal viral systems and how these systems may be used to approach the question of cellular regulation. Most information on the regulation of metabolic processes in eukaryotic cells comes from the study of bacteria and from the successful application of this knowledge to higher systems. However, differences in regulation of the translation of genetic information from the messenger RNA into protein may be expected between prokaryotes and eukaryotes. Due to the short half-life of prokaryotic mRNAs, transcription has been considered as the main mechanism controlling gene expression. Nevertheless, during recent years firm evidence has been accumulated for additional regu latory factors operating during translation. This topic was recently reviewed by HASELKORN and ROTHMAN-DENES (1973) and by KOZAK and NATHANS (1972)."

In lymphoiden Zellen Tb-sensibilisierter Meerschweinchen sind sessile Antikorper vorhanden, die in der Lage sind nach Kontakt mit Tuberkulin Komplement zu binden. Dieser Nachweis ist sowohl fluorescenzserologisch als auch - unter Verwendung von Extrakten aus solchen Zellen - mit der Hamagglutination und der Coombs-Technik oder mit dem Konglutinations- verfahren moglich. Sie konnen ferner mit dem Hamaggregationsverfahren nachgewiesen werden. Die sessilen Antikorper besitzen mindestens zwei, nach ihrer immunologischen Spezifitat und dem Mechanismus ihrer cytolytischen Funktion distinkte immunologische Spezifitaten. Die eine ist gegen den Haupt- bestandteil von Alttuberkulin (Tuberkulopolysaccharide) und die andere gegen den von gereinigtem Tuberkulin (Tuberkuloproteine) gerichtet. Beide Anti- korper konnen auf weisse Zellen nicht sensibilisierter Tiere ubertragen werden. Sie sind mercaptoathanolempfindlich und konnen deswegen den Antikorpern vom 19 S-Typ zugerechnet werden. Sie sind nicht identisch mit den cytophilen Antikorpern; auch scheint keine direkte kausale Beziehung zur Tuberkulin- Hautreaktion zu bestehen. Ihre mogliche Bedeutung wird diskutiert. Lymphoide Zellen von Tb-sensibilisierten Meerschweinchen enthalten ausserdem noch einen Faktor, der in vitro Agglutinationsreaktion und in vivo PCA-Reaktionen hemmt. Literatur BAlL, 0.: Ubertragung der Tuberkulinempfindliehkeit. Z. Immun.-Forseh. 1. Orig. 4,470 (1910). BLAZKOVEC, A. A., E. SORKIN, and J. L. TURK: A study of the passive eellular transfer of loeal eutaneous hypersensitivity. Int. Areh. Allergy 27, 289 (1965). BLOOM, B. R., and B. BENNETT: Meehanism of areaction in vitra associated with delayed type hypersensitivity. Scienee 153, 80 (1966). - - Delayed hypersensitivity in vitra: the meehanism of inhibition by antigen of eell migration. Fed. Prae. 25, 355 (1966).

The study of streptococcal infections and their sequelae has in the last two decades yielded several important findings on the biological properties of cellular and extracellular products of group A streptococci. These findings have contributed to a better knowledge of the pathological reactions occurring in the macroorganism during host-parasite interactions. Nevertheless, the pathogenesis of streptococcal infections is not fully understood. So far there has been no success in eliciting experimentally, either through the action of the substances isolated from the cell, or from broth culture filtrate of group A streptococci, symptoms that are fully identical with any type of acute streptococcal infection. It also has not been possible to explain the mUltiplicity of clinical and histological changes caused by streptococci as being due solely to anyone of these substances or a combination thereof. The same applies to the sequelae of streptococcal infections, rheumatic fever and acute glomerulonephritis. We do not know how the group A strepto coccus elicits these diseases and we have only a partial understanding of the pathological processes, initiated by this streptococcus, and resulting in cardiac or renal lesions. It is clear that an organism infected by streptococci is exposed to the action of a complex of substances. A more detailed recognition of the biological activity of the single components and their combination under defined experimental conditions may be capable, it is hoped, to explain the pathologic processes triggered in the course. of the development of group A streptococcal infection."

"When we give a definition it is for the purpose of using it." HENRI POINCARE in Science and Method A. Objectives The first version of this paper was written to introduce new students and fellows of my laboratory to the mysteries of herpesviruses. Consonant with this design sections dealing with well documented data were trimmed to the bone whereas many obscure phenomena, controversial data and seemingly trivial observations were discussed generously and at length. There is some doubt as to whether it was meant to be published, but it was not a review. The objective of reviews is frequently to bring order. But alas, even the most fluent summation of credible data frequently makes dull reading and too much plausible order, like very little entropy in chemical reactions, is not the most suitable environment on which to nurture the urge to discover. This version is more charitable but not less inbalanced. The bibliography reflects the intent of the paper and was updated last in December of 1968. It should be obvious without saying that no single account such as this can do justice or injustice, as the case may be, to the several hundred papers published on herpesviruses each year or to the many thousand papers published on herpesviruses since the first of the members of the family was experimentally transmitted to a heterologous host more than half a century ago (GRUTER, 1924). B. Definition 1.

Ever since arbovirus infections became known and their relative importance assessed, experiments were designed to elucidate the mode of transmission and the most important natural hosts responsible for perpetuating the infection in nature. Human infections and the disease in wild rodents, birds, and domestic animals were studied in relation to viremia and distribution of the infectious agent in the organism. With increasing epidemiological studies it became apparent that the neural manifestations of the disease are very uncommon, confined only to a small percentage of individuals of the most susceptible species. Various factors have been proposed to explain why in certain instances the virus becomes establish ed in the central nervous system and causes a serious or lethal disease. For example, differences in the virulence of the virus strains, varying susceptibility of individuals of one species, or intercurrent circumstances facilitating access of the virus to the central nervous system were alleged. Also, various possible routes of entry of the virus into the brain and spinal cord have been considered."

Expression of an immune response is the net result of complex synergis tic and antagonistic activities performed by a variety of cell types. It includes macrophages, T and B populations which may interact in performance of a response, and suppressor cells interfering with it. Accordingly, a lack of res ponse may not necessarily indicate absence of immunocompetent cells, but rather nonexpression of competence. Thus, one should consider two possible situations, which are by no means mutually exclusive, to account for immuno logic unresponsiveness: (a) one or more of the cell populations composing the synergistic unit is absent or immature, and (b) an antagonistic unit which interferes with the response is dominating. In view of this, an approach to development of immune reactivity necessitates parallel surveys of development of cells with the potential to perform, as well as of cells which can suppress the response. Classification of the various cell types has been based so far on their phenotypic properties (e. g., membrane antigen markers, cell receptors, pro duction and secretion of immunoglobulins, etc. ). Genotypically, T and B cells may represent either separate, independent cell lines, or different stages of development within the same cell lineage."

Phenomena as diverse as tuberculin sensitivity, delayed sensitivity to soluble proteins other than tuberculin, contact allergy, homograft rejection, experimental autoallergies, and the response to many microorganisms, have been classified as members of the class of immune reactions known as delayed or cellular hypersensitivity. Similarities in time course, histology, and absence of detectable circulating immunoglobulins characterize these cell-mediated immune reactions in vivo. The state of delayed or cellular hypersensitivity can be transferred from one animal to another by means of sensitized living lymphoid cells (CHASE, 1945; LANDSTEINER and CHASE, 1942; MITCHISON, 1954). The responsible cell has been described by GOWANS (1965) as a small lymphocyte. Passive transfer has also been achieved in the human with extracts of sensitized cells (LAWRENCE, 1959). The in vivo characteristic of delayed hypersensitivity from which the class derives its name is the delayed skin reaction. When an antigen is injected intradermally into a previously immunized animal, the typical delayed reaction begins to appear after 4 hours, reaches a peak at 24 hours, and fades after 48 hours. It is grossly characterized by induration, erythyma, and occasionally necrosis. The histology of the delayed reaction has been studied by numerous investigators (COHEN et al. , 1967; GELL and HINDE, 1951; KOSUNEN, 1966; KOSUNEN et al. , 1963; MCCLUSKEY et al. , 1963; WAKSMAN, 1960; WAKSMAN, 1962). Initially dilatation of the capillaries with exudation of fluid and cells occurs.

The processes involved in herpesvirus replication, latency, and oncogenic transformation, have, in general, been rather poorly defined. A primary reason for this is the size and complexity of the herpesvirus genome. Undoubtedly, a better understanding of the functions of the viral genome in infected and transformed cells will be achieved through studies with temperature-sensitive (ts) mutants of herpesviruses since, theoretically, any essential gene function can be affected by mutants of this type. A. The Herpesviruses A consideration of the genetic analysis of members of the herpesvirus group necessitates a description, albeit brief, of the properties of the group and, most importantly, of their genetic material. The herpesviruses comprise a group of relatively large (100-150 nm), enveloped viruses. The envelope surrounds an icosahedral capsid enclosing a core which contains double stranded DNA (ROIZMAN, 1969). The group is thus defined on the basis of a common virion morphology. In addition to a common structure, members of the group share a number of biological properties such as a similar replicative cycle, the ability to cause latent and chronic infections, and the ability to induce antigenic modifications of infected cell membranes. Several herpes viruses have been associated recently with malignancies in man and animals (KLEIN, 1972). Herpesviruses are ubiquitous and have been described in over 30 different species (HUNT and MELENDEZ, 1969; WILDY, 1971; FARLEY et aI. , 1972; KAZAMA and SCHORNSTEIN, 1972; NAHMIAS et aI. , 1972; ROlZMAN et aI. , 1973). Their widespread occurrence in nature suggests a common ancestor.

Prominent progress in molecular biology was only made when it became possible to separate functionally distinct molecules by taking advantage of their biophysical properties. Likewise, the analysis of the functions of hetero geneous populations of immunocompetent cells, as to the functional properties of their various subpopulations, can not be done until these can be isolated in reasonably pure form by selective fractionation. During the last few years significant advances have been made in this field, and cells have been separated according to size, density or charge (MILLER et aI., 1969; SHORTMAN, 1968; ANDERSSON, 1973 c), or by taking advantage of more specific surface markers to allow selective depletion or enrichment of a given subpopulation of cells (WIGZELL and ANDERSSON, 1971). Although separation techniques have been used in a variety of cellular systems, they have been particularly useful in the study of reticuloendothelial cells and primarily in the study of cells partici pating in the immune responses. Quite extensive reviews have been written which well cover the methods used for separation of cells and the results obtained with the various approaches (WIGZELL and ANDERSSON, 1971; SHORTMAN, 1972). To review this work is becoming a more and more voluminous task. As data rapidly accumulate, we will not try to make such a complete review."

Immunoglobulin gene expression appears to include a number of unique features (Cohn, 1971; Gaily and Edelman, 1972; Hood et aI. , 1975). First, a variety of genetic and protein structural evidence suggests that two discrete genes - both a variable region gene and a constant region gene - specify each heavy chain and each light chain. This constitutes the twogene-one polypeptide hypothesis. Second, a single differentiated lymphocyte or plasma cell appears to express only one heavy chain allele and one light chain allele at a time. This is the only example of allelic exclusion known in mammalian cells except for X chromosome inactivation. Third, during the course of lymphocyte differentiation, there may be a switch of the heavy chain constant region gene expression but no change in the heavy chain variable region gene expression. Rarely, normal or malignant cells have been found which express two different heavy chain subclasses simul taneously (e. g. see Sledge et aI. , 1976). Fourth, the vast number of different antibodies which can be made by an individual animal has raised the question of whether the generation of diversity occurs during evolution or within the animal, i. e. germ line vs somatic variation. Other aspects of immunoglobulin gene ex pression may be similar to regulation of gene expression in many eukaryotic cells.