To lose is human, to win is fortune, but to try is our destiny. EARL C. SUITOR, JR. The idea of a Symposium on "Arthropod Cell Cultures" started in July of 1969 shortly after the untimely death of our colleague, EARL C. SUITOR, JR. , at the age of 38. At first we thought an afternoon or evening session would be sufficient, but we were soon convinced that the scope of the Symposium should be greatly enlarged. Interest in this topic was increasing at an astonishing rate. Since EARL SUITOR had made a distinct imprint in this new field, many scientists who knew him well or just casually wished to honor him in this manner. EARL SUITOR was born and raised in New England and received a B. S. degree in bacteriology from the University of Massachusetts in 1952. As a spirited young man, he enlisted in the U. S. Navy to see the world. Instead, he was assigned for most of his four-year "hitch" to the Naval Medical Research Institute. I met him there in 1954, an enthusiastic and imaginative young fellow with many interests, an avid reader of the classics, an occasional writer of poetry, who blended his interest in scientific literature with that of Science Fiction. In 1956, EARL left the Navy to attend George Washington University, where he earned an M. S. degree in 1958 and a Ph. D. degree in 1963.

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* Discusses human, mammalian, insect and plant viruses in invertebrate cell culture systems* Addresses the commercial application of these systems in biotechnology and insect pest control* Brings together for the first time in over two decades the large body of information and significant achievements in the field

Cells and Tissues in Culture: Methods, Biology, and Physiology, Volume 3 focuses on the applications of the methods of tissue culture to various fields of investigation, including virology, immunology, and preventive medicine. The selection first offers information on molecular organization of cells and tissues in culture and tissue culture in radiobiology. Topics include cellular organization at the molecular level, fibrogenesis in tissue culture, effect of radiation on the growth of isolated cells, and irradiation of the selected parts of the cell. The publication then considers the effects of invading organisms on cells and tissues in culture and cell, tissue, and organ cultures in virus research. The book elaborates on antibody production in tissue culture and tissue culture in pharmacology. Discussions focus on early attempts at in vitro studies, tissue culture in the study of pharmacologically active agents, and methods of assessment of drug activity. The text also reviews invertebrate tissue and organ culture in cell research; introduction and methods employed in plant tissue culture; and growth, differentiation and organogenesis in plant tissue and organ cultures. The selection is a vital source of data for readers interested in the culture of cells and tissues.

The study of the genetic regulation of immune response to natural multidetermi nant immunogens was undertaken by the method of bidirectional selective breed ing of High or Low antibody responder lines of mice. Five Selections are described: Selection I, carried out for agglutinin responsiveness to sheep erythrocytes and pigeon erythrocytes alternated in each generation. Selection II, carried out for agglutinin responsiveness to sheep erythrocytes repeated in each generation. Selection III and Selection IV performed respectively for agglutinin response to flagellar or somatic antigens of Salmonella typhimurium and Salmonella oranienburg alternated in each generation. Selection V, performed for passive agglutinin response to bovine serum albumin and rabbit gamma globulin alternated in each generation. In each Selection the character investigated is polygenic. High and Low responder lines diverge progressively during the selective breeding. The maximal interline separation (selection limit) is reached in the 7th-16th generations. High and Low responder lines at selection limit are considered homozygous for the character submitted to se~ection. Their variance is therefore only due to environ mental effects. The difference in agglutinin titre between High and Low lines is 220-fold in Selection I, 103-fold in Selection II, 90-fold in Selection III, 85-fold in Selection IV and 275-fold in Selection V. The partition of genetic and environmental variances in the foundation popu lations of the five Selections is established. The proportion of genetic variance is 60% in Selection I; 49% in Selection II; 51% in Selection III; 47% in Selection IV and 76% in Selection V.

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 expression of many bacterial genes adapts itself in an almost in stantaneous and reversible way to specific environmental changes. More specifically, the concentration of a number of metabolites, a function of the amounts of enzymes involved in their synthesis or degradation, in turn retroacts on the rate of synthesis of these enzymes. The genetic bases for this regulation were established by JACOB and MONOD (1961). These authors also showed how the known elements of these regulatory mechanisms could be connected into a wide variety of circuits endowed with any desired degree of stability, in order to account for essentially irreversible processes like differentiation (MONOD and JACOB, 1961). The general principles used by JACOB and MONOD in their study of negative regulation were extended to positive regulation by ENGLESBERG et al. (1965). An independent approach permitted the discovery of positive controls in temperate bacteriophages (see below, III). Each control operation is mediated by a pair of complementary genetic elements (hereafter called "control cell"): a control gene which produces a l control (or regulator) protein and a control site which is the target for the regulator protein. Negative control means that the control protein (repressor) prevents gene expression. One deals with positive control when the control protein (activator) is necessary for this expression. It has become apparent that, as initially postulated by JACOB and MONOD, control of gene expression operates, at least to a large extent, at the transcriptional level.