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Showing papers in "Annual Review of Microbiology in 1986"


Journal ArticleDOI
TL;DR: The role of environmental exposures in the development of phylogeny is studied in the context of infectious disease and infectious disease.
Abstract: INTRODUCTION . . . . . . . . . . . . . . . .. ..... . . . . . . . . .. . . . . . .. . . . . . . . . . . . . . . . . . . . . .. . ...... .. . . . . . . .... . . . . . 338 MOLECULAR PHYLOGENY AND MICROBES . . . . . . . . . . . .. . . . . . . . . .... . . ... . . . . .... .. . . . . . 338 Ribosomal RNAs as Indicators of Phylogeny.. . . . ..... . . . . .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338 Analysis of Population

1,089 citations


Journal ArticleDOI
TL;DR: The aim of this monograph is to provide a discussion of the phytochemical properties of hydrogen, as well as some of the properties of chlorine, which have been studied in greater detail in the context of an open-air setting.
Abstract: SURVEY AND PROPERTIES OF ACETOGENS . . . . . . ... . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . 418 THE WOOD PATHWAY OF AUTOTROPHIC FIXATION OF CO2 INTO ACETATE . . . . . . . . . . . . . . . . . . . . . . . .. .. . . . . . . . . . . . . . . . . . . . . . .. .. . . . . . . . . . . . . . .... . . . . . . . . . . . 424 O utline of the Pathway..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424 Formate Dehydrogenase ... . . . . . . . . . . . . . . . . . . . . . . .. .. ...... . . . . . . . . . . .. .... . . . . . . . . . . .. .. ....... . 426 Tetrahydrofolate Enzymes . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . .. . . . . . 430 Corrinoid Proteins and Methyltransferase . . . . . . . . .. . .... . . . . . . . . . . ... . ..... .. . . . . . . . . . . ... . . 431 Carbon Monoxide Dehydrogenase and CO Dehydrogenase Disulfide Reductase.... 432 Hydrogenase and Energy Generation in Acetogens. . . . . . . . . . . ...... . . . . . . . . . . . . . . . . . . . . . . . 435 Methanol as a Precursor to Acetate....... 437 ACETYL COENZYME A AS PRECURSOR OF CELL CARBON IN ACETOGENS . . . . . . ....... . . . . . . . . . . . . . . . . .. ..... ...... . . . . . . . . ...... . ... . . . . . 438 ECOLOGICAL ASPECTS OF ACETOGENS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441 CONCLUDING REMARKS . . .. . . . . . . . . . . . ... . . . . . . . . . . .. . . .. . . . . .. . . . . .. .. . ... . ... . . .. . 442

574 citations



Journal ArticleDOI
TL;DR: The search for the “missing link” in the mechanism of Mercury’s reprograming continues to be a major challenge.
Abstract: INTRODUCTION...... . . . . .... . . . . . . . . . . . . . . . . . .. ...... . . . . . . . . . . . .... . . . .. ........ .. . 607 Occurrena of Mercury in the Environment 607 Incidence of the Mercury Resistance Phenotype 608 THE GRAM-NEGATIVE SySTEMS 609 The Structural Genes of the mer Loci 609 Regulation ...... . 618 Overview of Operon Function........ . . .. . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . .... . . . . .. . . . .. . . . . . . . . . 623 .. Evolutionary Considerations ... . . . ........ . . . . . . . . . . . . . . . . ..... . . . . . . . . ....... . . . . . . 624 THE GRAM-POSITIVE SySTEMS 626 Occurrence . . . " 626 Biochemistry.. . . . . 627 Genetics . ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627 CONCLUDING REMARKS 627

330 citations


Journal ArticleDOI
TL;DR: Revue concernant les donnees actuelles sur la lixiviation bacterienne des metaux a partir des minerais et la description des technologies microbiennes en developpement pour leur recuperation.
Abstract: Revue concernant les donnees actuelles sur la lixiviation bacterienne des metaux a partir des minerais et la description des technologies microbiennes en developpement pour leur recuperation

275 citations


Journal ArticleDOI
TL;DR: A comparison study of nonplasmid Multiple Resistance Transfer in Various Species of Streptococci and its effects on HemolYSin Genes in StreptOCOCCUS FAECallS shows how these effects can change over time.
Abstract: INTRODUCTION 636 IDENTIFICATION AND PROPERTIES OF Tn916 636 MECHANISM OF Tn916 MOVEMENT 642 OTHER CONJUGATIVE TRANSPOSONS 644 Tn918 and Tn919 ......... ...... 644 Nonplasmid Multiple Resistance Transfer in Various Species of Streptococci........ 645 COMMON ASSOCIATION OF Tc RESISTANCE WITH CONJUGATIVE TRANSPOSONS 650 SOME COMMON EFFECTS OF CONJUGATED TRANSPOSONS ON HEMOLYSIN GENES IN STREPTOCOCCUS FAECALlS 65 I HOST RANGE OF CONJUGATIVE TRANSPOSONS 652 POTENTIAL USES FOR CONJUGATIVE TRANSPOSONS IN GENETIC STUDIES.. . . . . . . ... . . . . . . . . . . . . . . .. . . . . . . . . .. . . . . . . . . . . . . . . . .. .. . . . .. . . . . ..... 652 CONCLUDING REMARKS 653

269 citations


Journal ArticleDOI
TL;DR: The Rhizosphere and Nodule Initiation are studied as well as other aspects of human evolution and natural selection that are relevant to the management of infectious disease and infectious disease.
Abstract: INTRODUCTION ......... . . . . . . . . . .... . . . . . . . . ......... ... . . . . ........ . . . . . .. . . . . . . . . ..... . . . . . . . .... 1 32 Establishment of Rhizobium Inoculants in the Field . . . .. . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .. 1 32 Characterization of the Indigenous Rhizobium Population . . . . .. . . . . . . . . . . . . . . . . . . ... .. . . 133 Genetic Exchange Among Rhizobia in Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... . . . . . . .. . . . . . . . 135 ECOLOGICAL FACTORS THAT AFFECT COMPETITION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 Environmental Factors...... .. . . . . ..... ...... . . .. . .. 1 36 Biological Factors . . . . . . . . . . .. . . . . . . . . ........ . . . . . . .. ........ . . . . ..... . . . . . . ...... . . . . ...... . . . . . 140 Other Factors. . . . . . . . . . . . . . . . . . . . . . . . . ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 COMPETITION IN THE RHIZOSPHERE . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . 143 Chemotaxis and Motility . . ...... . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Effect of the Rhizosphere . . ...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...... . . . . . ... . . . . . . . . . . . . 143 Attachment and Nodule Initiation ......... ..... ........ . ........ 144 Genetics of Nodule Initiation in Rhizobium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 HOST GENES THAT CONTROL NODULATION . . . . . . . . ..... . . . . . . . .... . . . . . . ..... . . . . . . . . 147 CONCLUSIONS . . ....... . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . 148

265 citations


Journal ArticleDOI
TL;DR: It is suggested that both gene transfer and acquisition of carbon, nitrogen, and energy represent physiological needs that may have contributed to the evolution of natural transformation.
Abstract: Natural transformation is widely distributed among bacteria. Its variations, in terms of specific mechanisms, may in part reflect responses to different selective pressures in different bacteria. We have suggested that both gene transfer and acquisition of carbon, nitrogen, and energy represent physiological needs that may have contributed to the evolution of natural transformation. While natural transformation was the first mechanism of genetic exchange to be detected, it is perhaps the least understood. Our understanding of the mechanism for uptake and incorporation of soluble DNA has increased significantly in the last two decades, but the overall picture of transformation as a biologically significant function is still unfolding. The mechanism by which DNA is released for transformation, the control of genes involved in DNA release and uptake, the potential for transformation in the natural environment, and the potential of natural transformation as a tool for other microbiological studies are but a few of the important issues that remain.

221 citations


Journal ArticleDOI
TL;DR: Plasmid·Chromosome Interaction 93 MAP COMPAR I SON S.INTRODUC][10N] .
Abstract: INTRODUC][10N .. . . . . . . . . ..... ... . .. ...... . . . . . . . . . . .. . . . . . . . . . . . . . . . .... ...... . . . . . . . . . . .. ... . . . . . . 79 GENETI C ANALY SI S OF PSEUDOMONAS SPECIES . . . . . . . . ... .. ... . . . . .. . . .. . .. ......... 8 1 Genetic Exchange Mechanisms i n Pseudomonas . .. ... .. .. .. . . . .... ... . ... .. 8 1 Comparison of Genomes . . . . . . . . . . . . . . .. . . . . .. .. . . .. . . . . . . . . . . . . . .. . . . . . . ..... . . ... . . .. . . . . . . . .. 83 SPE CIAL FEA TURE S OF THE PSEUDOMONAS GE NOME. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 Gene Arrangement 86 Plasmids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Plasmid·Chromosome Interaction 93 MAP COMPAR I SON S. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 DISCUSSION.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

220 citations


Journal ArticleDOI
TL;DR: Data obtained using several experimental methods indicate that crystal protein genes in many subspecies of BT that are toxic to lepidopterans are located on one or more large plasmids; in some subspecies, the gene may be located on the chromosome.
Abstract: Data obtained using several experimental methods (curing, transconjugation, cloning, and hybridization) indicate that crystal protein genes in many subspecies of BT that are toxic to lepidopterans are located on one or more large plasmids; in some subspecies, the gene may be located on the chromosome. Detailed mapping has shown that in three plasmids (each from a different strain) the genes are surrounded by multiple copies of two repeated DNA elements; the arrangement of these elements is the same in the three plasmids. An analysis of the sequence of one of these repeated DNAs strongly suggests that it contains a transposase. Thus, transfer of crystal protein genes between plasmids and/or between plasmids and the chromosome would be possible either by transposition or by recombinational events mediated by the repeated DNAs. Crystal protein genes have been cloned from several plasmids and were expressed in E. coli and B. subtilis, whereas two genes cloned from chromosomal preparations were not expressed. Some of the factors that regulate expression of a plasmid-borne gene in E. coli and B. subtilis have been identified. Very little is known about the role of sporulation genes in regulating expression of the crystal protein gene in B. subtilis or BT. In BT, expression may also be affected by genes on other plasmids. Three homologous crystal protein genes have been identified and cloned from subsp. kurstaki and thuringiensis; different strains of these subspecies may contain one, two, or three of these genes. It seems probable that additional gene families will be found, since the crystals of different subspecies contain immunologically distinguishable proteins. The DNA sequences of the three homologous genes have been published as has the sequence of the crystal protein gene from subsp. sotto. These four genes have regions of identity (the promoter region) and similarity (the N-terminal approximately 280 amino acids, the C-terminal half of the protein, and the terminator). It is interesting that the divergent portions of the molecules are not in precisely the same positions and that all overlap the toxin-encoding portion of the gene. It would be worthwhile to determine if the differences in the amino acid sequence are related to differences in the toxicity and/or the host range of the cloned genes, and to establish how the complement of genes in a given strain contributes to the overall toxicity of that strain.(ABSTRACT TRUNCATED AT 400 WORDS)

215 citations



Journal ArticleDOI
TL;DR: Information is provided on how to identify the phytochemical components of E.coliococci, which can cause diarrhoea, vomiting, and fever in animals and humans.
Abstract: INTRODUCTION . . .. . . .... . . . .. 185 DETAILED ANALYSIS OF A SELECTED STRAIN GROUP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 87 Bacterial Groupings and Sources 187 OMP Patterns, Isoenzymes, and Serotypes ...... ..... 1 88 Other Properties 193 CLASSICAL VERSUS NEWER METHODOLOGIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 Serology and Biotyping . .. ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 Other Classification Methods 199 Isoenzyme Analysis and OMP Patterns 200 VIRULENCE . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 Neonatal Meningitis 201 Urinary Tract Infections 203 Clonal Groupings and Virulence . . . . . . . . . . . .. : . . . . . . . . . .... . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 204



Journal ArticleDOI
TL;DR: Monoclonal antibodies and recombinant DNA technology have greatly facilitated the identification, isolation, and characterization of proteins that may be involved in invasion, and it is not yet known whether any of the molecules discussed here will prove to be effective immunogens.
Abstract: Studies on the morphology, cell biology, and immunology of invasion have characterized events that are now being studied at the molecular level. The initial events of invasion are receptor-specific. A determinant associated with Duffy blood group antigens is involved in the invasion of human erythrocytes by P. knowlesi and P. vivax. The Duffy Fya antigen has recently been identified and further characterization of its role in reception and invasion should now be possible. P. falciparum utilizes erythrocyte ligands that differ from those of P. knowlesi and P. vivax. Sialic acid and a trypsin-sensitive erythrocyte membrane component are important for invasion by P. falciparum parasites. There is evidence that at least two ligands are involved in invasion. For P. knowlesi there is a ligand for attachment, common to both Duffy-negative and Duffy-positive human erythrocytes, and a second ligand for invasion, which is found only on Duffy-positive human erythrocytes. P. vivax also appears to utilize two ligands, a Duffy-associated ligand and a ligand specific for reticulocytes. P. falciparum binds to sialic acid-dependent and sialic acid-independent trypsin-sensitive ligands. P. falciparum merozoites require erythrocyte sialic acid to varying degrees in order to invade; this indicates heterogeneity of the receptor mechanism. Monoclonal antibodies and recombinant DNA technology have greatly facilitated the identification, isolation, and characterization of proteins that may be involved in invasion. Molecules that may have invasion-related functions include those whose antibodies block invasion, those that bind to erythrocyte ligands important for invasion, those that appear on the merozoite surface, and those that appear to be inserted into the erythrocyte membrane at the time of invasion. It has not been possible to identify a definite function for any of the molecules identified thus far. No monoclonal or polyclonal monospecific antibody has been identified that reacts specifically over the surface of the apical region of the merozoite where junction formation occurs. Identification of molecules responsible for apical attachment and junction formation will be important for our understanding of invasion. In terms of vaccine development, it is not yet known whether any of the molecules discussed here will prove to be effective immunogens. It is clear from the data obtained with the 140-kd protein of P. knowlesi that antigenic variation poses a potential problem for vaccine development. As the molecular events responsible for invasion become better understood, novel ways may be devised to interfere with the process and prevent the disease.


Journal ArticleDOI
TL;DR: Revue des connaissances actuelles sur les immuncomplexes dans des infections bacteriennes chroniques, insistance sur l'infection a Pseudomonas aeruginosa dans les poumons de sujets atteints de mucoviscidose.
Abstract: Revue des connaissances actuelles sur les immuncomplexes dans des infections bacteriennes chroniques. Insistance sur l'infection a Pseudomonas aeruginosa dans les poumons de sujets atteints de mucoviscidose. L'endocardite infectieuse et la lepre sont aussi discutees

Journal ArticleDOI
TL;DR: The structure of the immune system and its role in disease and infection are studied in detail in this chapter to discuss immunity and infection.
Abstract: INTRODUCTION 479 THE PATHOGENS 480 Bacteria.. . . . ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . .. . . . . . . . . . . . . . ....... .. ....... 480 Viruses..... ..... 481 Clinical Manife stations 482 THE HOST 482 Nonimmune Defense 483 Immune Defense , 485 ANTIGENIC STRUCTURE 488 THE DISEASE PROCESS .... ..... ..... 491 Transmission ....... . .... . 491 Pathogenesis... ....... ... .... 491 FINAL COMMENTS 497

Journal ArticleDOI
TL;DR: The present work aims to demonstrate the efforts toward in-situ regulation of Gene Expression in KlebsiElLA and to describe the efforts towards this goal through a probabilistic approach.
Abstract: INTRODUCTION 525 nif GENE ORGANIZATION IN KLEBSIElLA 526 ORGANIZATION OF THE nifGENES OF RHODOPSEUDOMONAS CAPSULATA.. 529 nif Genes on Cloned DNA Fragments 529 Chromosome Mobilization 533 Regulation of Gene Expression 536 ORGANIZATION OF THE nif GENES OF CY ANOBACfERIA 537 CONCLUSIONS 542

Journal ArticleDOI
TL;DR: The Nervous System as a TARGET for VIRUS INFECTions and the Effects of PERSISTENCE and Demyelination are discussed.
Abstract: INTRODUCTION . THE NERVOUS SYSTEM AS A TARGET FOR VIRUS INFECTIONS .. MECHANIS:MS FOR RNA VIRUS PERSISTENCE "". PERSISTENCE IN THE CENTRAL NERVOUS SYSTEM OF RNA VIRUSES OF DIFFERENT FAMILIES . Picornaviridae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Togaviridae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Coronaviridae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Arenaviridae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rhabdoviridae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Paramyxoviridae . Retroviridae . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . EFFECTS OF PERSISTENT VIRAL INFECTIONS ON THE NERVOUS SYSTEM . Maturation Disturbances . Demyelination . Spongiform Changes in the Central Nervous System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Altered Neuronal Function . . .. . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CONCLUDING REMARKS .

Journal ArticleDOI
TL;DR: Hydrolytic Reactions of the gas phase of the greenhouse process are studied to establish an understanding of the mechanism behind the hydrolysis of gas mixtures.
Abstract: METABOLIC ACTIVITIES OF THE GASTROINTESTINAL MICROFLORA ........ . Hydrolytic Reactions: Glycosidases . Reductas.es . Other Bacterial Reactions . Amines .

Journal ArticleDOI
TL;DR: A Light-Driven Chloride Pump, Anriport Systems for Phosphorylated Compounds, and A Plasmid-Encoded Arsenical Pump are described.
Abstract: CATION TRANSPORT SYSTEMS . 264 Sodium Transport Systems 264 Potassium Transport Systems 271 ANION TRANSPORT SySTEMS. . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 A Light-Driven Chloride Pump 275 Anriport Systems for Phosphorylated Compounds 276 A Plasmid-Encoded Arsenical Pump 279 CONCLUDING REMARKS . ..... . .. .... .. . . . . . . . . . . . .. 281

Journal ArticleDOI
TL;DR: The new range of downward and upward modulation in the levels of single enzymes and combinations of enzymes may contribute to a better understanding of flux regulation and its influence on the overall physiology of an organism.
Abstract: In recent years more information about tryptophan biosynthesis in eukaryotic microorganisms has become available. The emphasis has been on genetics and biochemistry of the pathway. Eukaryotes manifest a trend toward fewer genes and toward multifunctional proteins, while prokaryotes have a greater tendency toward separate activity domains but the genes tend to be clustered genetically. Cloning of various structural tryptophan biosynthetic genes and studies on their expression in homologous and heterologous hosts have made it possible to analyze promoter structures in detail and to define structural elements involved in regulated gene expression. Comparisons of homologous genes from different organisms have highlighted the conservation of the activity domains or parts therefrom involved in the catalysis of single steps. These studies also point to a stringent maintenance of domains responsible for protein-protein aggregation. Physiological studies will be facilitated by the availability of single cloned genes and especially the artificial gene cluster containing all five TRP genes from yeast. The range of physiological manipulation has thus been enormously broadened. With chromosomal mutations it has been possible to study primarily downward modulation of a pathway. We can now initiate studies on upward modulation, since enzyme levels appear to increase in proportion to gene dose. The new range of downward and upward modulation in the levels of single enzymes and combinations of enzymes may contribute to a better understanding of flux regulation and its influence on the overall physiology of an organism.



Journal ArticleDOI
TL;DR: A model for isotype-specific regulation of IgA synthesis by Fc alpha R+ T cells is suggested, which may involve a DNA switch rearrangement or the maturation of previously switched cells and appears to be mediated via an IgABF with enhancing activity.
Abstract: The data presented here suggest a model for isotype-specific regulation of IgA synthesis by Fc alpha R+ T cells (Figure 1). Immature mIgM+ +/- mIgD+ B cells are induced by T switch cells to express cell surface IgA (a phenotypic switch). If the T switch cell induces mIgA expression via a long primary RNA transcript from an unrearranged C alpha allele, the hypothetical intermediate switch B cell results (step 1); this may be the mechanism of heavy chain expression in memory B cells that express low levels of Ig. Alternatively, T switch cells may induce a DNA rearrangement in the CH locus of the B cell (a genotypic switch), which results in a deletion of all CH loci except C alpha (step 2). TH inducer cells promote maturation of mIgA+ B cells to IgA-secreting plasma cells. This may involve a DNA switch rearrangement (step 3) or the maturation of previously switched cells (step 4), and appears to be mediated via an IgABF with enhancing activity. Not shown in this figure, but inherent in this model, is a suppressive regulatory arm that may be mediated via IgABF with suppressive activity released from Fc alpha R+ suppressor T cells. Due to the presence of Fc alpha R on a variety of cell types, IgABF may suppress synthesis of IgA by acting not only on mIgA+ B cells but also on regulatory cells (T cells, B cells, and macrophages) bearing IgA bound to Fc alpha R. If the IgA system is analogous with the IgE system, mIgA-bearing B cells may be the direct target of IgABF. Binding of Ig to FcR has been shown to (a) increase the number of Fc receptors per cell, (b) enhance the number of cells expressing Fc receptors, (c) induce the release of IgBF that either suppress or enhance Ig secretion, and (d) effectively convert surface Ig- cells into surface Ig+ cells that are therefore receptive to IgBF. Thus, FcR+ cells may interact with IgBF and Ig via a regulatory network to stimulate or inhibit the immune response in an isotype-specific manner. Cell surface molecules (mIg, FcR) may serve as sensors that allow the cell to detect and respond to fluctuations in the levels of immune mediators that serve to modulate Ig synthesis and secretion. The relationship between IgBF and FcR is not known, nor is it known whether Fc receptors expressed by different cell types are encoded by the same gene and are controlled similarly.(ABSTRACT TRUNCATED AT 400 WORDS)