An analysis of unstirred layers in series with "tight" and "porous" lipid bilayer membranes

The present experiments were designed to evaluate the effective thickness of the unstirred layers in series with native and porous (i.e., in the presence of amphotericin B) lipid bilayer membranes and, concomitantly, the respective contributions of membranes and unstirred layers to the observed resistances to the diffusion of water and nonelectrolytes between aqueous phases. The method depended on measuring the tracer permeability coefficients for the diffusion of water and nonelectrolytes (P_DDi, cm sec^-1) when the aqueous phase viscosity (η) was increased with solutes having a unity reflection coefficient, such as sucrose or dextran. The effective thickness of the unstirred layers (α^t, cm) and the true, or membrane, permeability coefficients for diffusion of water and nonelectrolytes (P_mmi, cm sec^-1) were computed from, respectively, the slope and intercept of the linear regression of 1/P_DDi on η. In both the native and porous membranes, α^t was approximately 110 x 10^-4 cm. The ratio of P_f, the osmotic water permeability coefficient (cm sec^-1) to P_mmH2O was 1.22 in the native membranes and 3.75 in the porous membranes. For the latter, the effective pore radius, computed from Poiseuille's law, was approximately 5.6 A. A comparison of P_mmi and P_DDi, indicated that the porous membranes accounted for 16, 25, and 66% of the total resistance to the diffusion of, respectively, H₂O, urea, and glycerol, while the remainder was referable to the unstirred layers.     

"Dinoflagellate Sterols" in marine diatoms

Sterol compositions for three diatom species, recently shown to contain sterols with side chains typically found in dinoflagellates, were determined by HPLC and ¹H NMR spectroscopic analyses. The centric diatom Triceratium dubium (= Biddulphia sp., CCMP 147) contained the highest percentage of 23-methylated sterols (37.2% (24R)-23-methylergosta-5,22-dienol), whereas the pennate diatom Delphineis sp. (CCMP 1095) contained the cyclopropyl sterol gorgosterol, as well as the 27-norsterol occelasterol. The sterol composition of Ditylum brightwellii (CCMP 358) was the most complex, containing Δ⁰- and Δ⁷-sterols, in addition to the predominant Δ⁵-sterols. A pair of previously unknown sterols, stigmasta-5,24,28-trienol and stigmasta-24,28-dienol, were detected in D. brightwellii and their structures were determined by NMR spectroscopic analysis and by synthesis of the former sterol from saringosterol. Also detected in D. brightwellii was the previously unknown 23-methylcholesta-7,22-dienol.     

"Second" and "third operator" of the lac operon: an investigation of their role in the regulatory mechanism.

The influence of the two operator-like regions lying within or near the lac regulatory region on the binding of lac repressor to lac operator has been investigated. λdlac phages deleted either for the “second operator” in the beginning of the Z gene or deleted for the “third operator” at the end of the I gene were constructed. In in vitro binding experiments it could be shown that the deletion of secondary repressor binding sites from the lac regulatory region does not significantly alter the stability of the repressor—operator complex. Measuring the rate constant of association of repressor with operator in the presence of a 150-fold excess of unspecific DNA, we observed a concentration-dependent effect of the unspecific DNA, although the ratio of operator to non-operator DNA was kept constant. A small effect of the secondary binding sites is seen on the rate of association of repressor with operator, indicating that the secondary binding sites might play a role in facilitating association of repressor with operator under _{in vivo} conditions.     

Widespread presence of "bacterial-like" PPP phosphatases in eukaryotes

Background

In eukaryotes, PPP (p rotein p hosphatase P) family is one of the two known protein phosphatase families specific for Ser and Thr. The role of PPP phosphatases in multiple signaling pathways in eukaryotic cell has been extensively studied. Unlike eukaryotic PPP phosphatases, bacterial members of the family have broad substrate specificity or may even be Tyr-specific. Moreover, one group of bacterial PPPs are diadenosine tetraphosphatases, indicating that bacterial PPP phosphatases may not necessarily function as protein phosphatases.

Results

We describe the presence in eukaryotes of three groups of expressed genes encoding "non-conventional" phosphatases of the PPP family. These enzymes are more closely related to bacterial PPP phosphatases than to the known eukaryotic members of the family. One group, found exclusively in land plants, is most closely related to PPP phosphatases from some α-Proteobacteria, including Rhizobiales, Rhodobacterales and Rhodospirillaceae. This group is therefore termed Rhi zobiales / Rh odobacterales / Rh odospirillaceae-l ike ph osphatases, or Rhilphs. Phosphatases of the other group are found in Viridiplantae, Rhodophyta, Trypanosomatidae, Plasmodium and some fungi. They are structurally related to phosphatases from psychrophilic bacteria Shewanella and Colwellia, and are termed She wanella-l ike ph osphatases, or Shelphs. Phosphatases of the third group are distantly related to ApaH, bacterial diadenosine tetraphosphatases, and are termed A paH-l ike ph osphatases, or Alphs. Patchy distribution of Alphs in animals, plants, fungi, diatoms and kinetoplasts suggests that these phosphatases were present in the common ancestor of eukaryotes but were independently lost in many lineages. Rhilphs, Shelphs and Alphs form PPP clades, as divergent from "conventional" eukaryotic PPP phosphatases as they are from each other and from major bacterial clades. In addition, comparison of primary structures revealed a previously unrecognised (I/L/V)D(S/T)G motif, conserved in all bacterial and "bacterial-like" eukaryotic PPPs, but not in "conventional" eukaryotic and archaeal PPPs.

Conclusions

Our findings demonstrate that many eukaryotes possess diverse "bacterial-like" PPP phosphatases, the enzymatic characteristics, physiological roles and precise evolutionary history of which have yet to be determined.

     

Some further remarks "on testing hypotheses concerning standardized mortality ratios"

In testing the equality of any k standardized mortality ratios from p(?k) populations, Kupper and Kleinbaum (1971) pointed out that different test procedures are required for the two situations where the standard population is chosen independently of the p populations and where the standard is formed by pooling all p populations. Unfortunately, the test they propose for the latter situation is applicable only when k = p. The purpose of this paper is to describe an alternative procedure based on the general theories of Wald (1943) and Neyman (1949) which can be used if the standard is a pooled one even when k < p.     

Two different ionic mechanisms generating the spike "positive" afterpotential in molluscan neurons

The ionic bases of the "positive" afterpotential (ap) have been examined in the so-called DInhi neurons of the central nervous system of Cryptomphallus aspersa. In these cells E_K has been determined and its value compared with the equilibrium, potential of the ap (E_ap). It has been found that in half of the studied cells the E_K value is very close to E_ap whereas in another half, the difference (E_K - E_ap) is large and amounts to circa -10 mv. The effects of changes in the concentration gradients of K⁺, Cl^-, and Na⁺ were assayed in both groups of cells. When the [K_i/[K]_o ratio is reduced in both groups of neurons, the ap amplitude and the E_ap diminished. In cells displaying a large (E_K - E_ap), Cl-free Ringer's solution diminished the ap amplitude and E_ap, but produced no effect in the neurons with a reduced (E_K - E_ap). A similar effect was observed if [Cl], was increased by intracellular injection of NaCl. Changes in both [Na]_o and [Na]_i were ineffective. It is concluded that K⁺ is the only ion involved in the origin of the ap in the groups of cells with a low value for (E_K - E_ap). On the contrary, the ap of the neurons presenting large (E_K - E_ap) is produced by a simultaneous increase in the fluxes of both K⁺ and Cl^-.     

Apis iridescent virus and "clustering disease" of Apis cerana

NPV of Spodoptera littoralis was completely inactivated in vitro following 10 min of exposure to a temperature higher than 90°C, but survived 3 weeks at ?20°C. At pH 12, some 75% of the infectivity was lost. Measurable proteolysis in vitro of the polyhedral protein by a larval midgut extract could be obtained only when the pH of the reaction mixture was raised to an unnatural level of 10.5, the natural pH of the midgut content being 8.5 or 9.5 according to different authors. The plant growth retardant Phosfon synergized mortality caused by the NPV. The virus could be cross-transmitted to two congeneric species of Spodoptera (S. exigua and S. litura), but could not infect any of four tested species belonging to other genera of the Moctuid family.     

Evidence for a single catalytic site on the "beta-D-glucosidase-beta-D-galactosidase" of almond emulsin.

An isoenzyme of glycosidase obtained from almond emulsin, which is both a β-d-glucosidase and a β-d-galactosidase, has now been shown to possess β-D-fucosidase activity. It has been concluded that all three activities reside in a single catalytic site for the following reasons. (i) d-Glucosylamine, d-galactosylamine, and d-fucosylamine (a newly discovered potent inhibitor of this enzyme) each act competitively against all three of the substrates. (ii) Any given inhibitor exhibits the same K_i value when tested in the presence of any of the three substrates, (iii) When the enzyme is incubated with any two of the p-nitrophenyl glycoside substrates, at or above their respective K_m values, the rate of p-nitrophenol formation is not additive, but rather is equal to the value calculated on the basis of the individual K_m values and relative maximum velocities.     

Occurrence in vivo of "hidden breaks" at specific sites of 26 S ribosomal RNA of Musca carnaria.

A fragmentation process occurs in 26 S ribosomal RNA of mature cytoplasmic ribosomes of Musca carnaria. It consists of the sequential appearance of three “hidden breaks” that fragment 26 S rRNA (M_r = 1.42 × 10⁶) into four pieces with approximate molecular weights of 0.68 × 10⁶, 0.35 × 10⁶, 0.29 × 10⁶ and 0.096 × 10⁶, respectively. This fragmentation was not observed in 17 S rRNA (M_r = 0.74 × 10⁶).Extremely mild treatment of newly assembled ribosomes with pancreatic RNAase reproduces the 26 S rRNA fragmentation phenomenon in vitro in the same way as it occurs in vivo.This evidence is discussed in relation to the secondary structure of 26 S rRNA and its binding with specific ribosomal proteins.     

The "cytochrome b5 fold": structure of a novel protein superfamily

Selective proteolysis allows the isolation of a heme-binding fragment spectrally similar to microsomal cytochrome b₅ from both baker's yeast flavocytochrome b₂ (a flavohemoprotein) and liver sulfite oxidase (a molybdoprotein). The amino acid sequences of these two fragments have been published separately (Guiard &; Lederer, 1976,1979). We present in this paper an alignment of those sequences with that of microsomal cytochrome b₅. The structural consequences of the similarity between the three primary structures are discussed in the light of the cytochrome b₅ three-dimensional model (Mathews et al., 1971,1972,1975; Mathews &; Czerwinski, 1976).It is concluded that the three heme-binding proteins are in all probability the products of a divergent evolution from a common ancestor and that they must present a basically similar backbone with some surface alterations. We propose to name this backbone the “cytochrome b₅ fold”. The comparison of the three proteins suggests hypotheses concerning the molecular surface areas involved in the recognition of cytochrome c (the common acceptor) and of the respective reductase (flavo- or molybdoprotein).In addition, our results suggest that at some point in evolution, several copies of an initial hemoprotein gene were formed in the cellular genome. Subsequently, one copy was fused with the gene for another function: a flavoreductase in yeast cells or a molybdoreductase in hepatic cells.     

The evolution of "deformed" brains in ant-like stone beetles (Scydmaeninae, Staphylinidae)

We present the first study of the central nervous system of adult representatives of Scydmaeninae. Histological staining, scanning electron microscopy and computer-based 3D reconstruction techniques were used to document the shape and configuration of the major cephalic elements of the central nervous system and to explain its anomalies compared to other Coleoptera. For the first time we report the presence of cephalic glands in ant-like stone beetles: in Scydmaenus (Cholerus) hellwigii openings of voluminous glands are located near the occipital constriction and their secretion accumulates in a large cavity of the dorsal head region. In Scydmaenus (Cholerus) perrisi the proto-, deuto-, tritocerebrum and the suboesophageal ganglion together form a large and compact ganglionic mass around the anterior foregut in the retracted neck region of the head. We exclude miniaturization as the driving force of the observed modifications. Comparative study of the head anatomy of S. perrisi, S. hellwigii, Scydmaenus (s. str.) tarsatus, Scydmaenus (Parallomicrus) rufus and Neuraphes elongatulus suggests a possible evolutionary scenario. We propose an evolutionary reversal hypothesis, involving a) the displacement and concentration of the cephalic central nervous system induced by the development of glandular cavities of the head, followed by b) a reduction of the glandular structures, without a secondary relocation of the cephalic CNS. The interpretation of head modifications in Scydmaeninae in the light of such a scenario may turn out as important for the reconstruction of the phylogeny and evolution of this highly successful group of beetles.     

Generic placement of the Neotropical species of " Phragmatobia" (Erebidae, Arctiinae), with a remarkable matrivorous species from the Peruvian Andes

Phragmatobia Stephens is briefly reviewed and a diagnosis is provided. The South American species currently placed in Phragmatobia Stephens are revised to two new genera, Andesobia Schmidt and De Freina, gen. n., and Patagobia Schmidt and De Freina, gen. n. (subtribe Spilosomina). Both Andesobia and Patagobia exhibit adaptations to high altitude habitats, including micropterous females in Andesobia (Patagobia females are unknown) and diurnal flight of males. The adults, immature stages, and mating behaviour of Andesobia jelskii (Oberthür, 1881) are described. Males of Andesobia jelskii enter the female cocoon to mate, and the micropterous, flightless females remain in the cocoon following oviposition where newly hatched larvae feed initially on the female’s body.Four species are included in Andesobia, Andesobia jelskii comb. n. (= Paracles imitatrix Rothschild, 1922, syn. n.), Andesobia flavata (Hampson, 1901), comb. n., Andesobia boliviana (Gaede, 1923), comb. n. (=Turuptiana flavescens Rothschild, 1933, syn. n.), and Andesobia sanguinea (Hampson, 1907), comb. n. Patagobia includes only Patagobia thursbyi (Rothschild, 1910), comb. n., and Patagobia thursbyi pluto Toulgoët is relegated to its synonymy. Patagobia shows affinities to Phaos Walker, 1855 of Australia, Metacrias Meyrick, 1886 of New Zealand, and Pseudophragmatobia Krüger, 2009 of South Africa, suggesting a common ancestry of circumantarctic origin. Phragmatobia karsholti Toulgoët, 1991 is transferred to Venedictoffia Toulgoët, comb. n., an unrelated genus that is removed from subtribe Arctiina and provisionally placed in the Phaegopterina. Phragmatobia oberthueri Rothschild, 1910, described from Tibet, is a synonym of Lachana alpherakii (Grum-Grzhimailo, 1891) [Erebidae: Lymantriinae], syn. n., comb. n.     

The "electrostatic-switch" mechanism: Monte Carlo study of MARCKS-membrane interaction

The binding of the myristoylated alanine-rich C kinase substrate (MARCKS) to mixed, fluid, phospholipid membranes is modeled with a recently developed Monte Carlo simulation scheme. The central domain of MARCKS is both basic (ζ = +13) and hydrophobic (five Phe residues), and is flanked with two long chains, one ending with the myristoylated N-terminus. This natively unfolded protein is modeled as a flexible chain of “beads” representing the amino acid residues. The membranes contain neutral (ζ = 0), monovalent (ζ = −1), and tetravalent (ζ = −4) lipids, all of which are laterally mobile. MARCKS-membrane interaction is modeled by Debye-Hückel electrostatic potentials and semiempirical hydrophobic energies. In agreement with experiment, we find that membrane binding is mediated by electrostatic attraction of the basic domain to acidic lipids and membrane penetration of its hydrophobic moieties. The binding is opposed by configurational entropy losses and electrostatic membrane repulsion of the two long chains, and by lipid demixing upon adsorption. The simulations provide a physical model for how membrane-adsorbed MARCKS attracts several PIP₂ lipids (ζ = −4) to its vicinity, and how phosphorylation of the central domain (ζ = +13 to ζ = +7) triggers an “electrostatic switch”, which weakens both the membrane interaction and PIP₂ sequestration. This scheme captures the essence of “discreteness of charge” at membrane surfaces and can examine the formation of membrane-mediated multicomponent macromolecular complexes that function in many cellular processes.     

Influence of the mutation "diabetes" on insulin release and islet morphology in mice of different genetic backgrounds

Mice, 7–8-mo old, of the C57BL/KsJ-db strain and homozygotic for the mutant gene db, exhibited marked hyperglycemia and moderately elevated serum insulin levels. Light and electron microscopy provided evidence of a slightly decreased proportion of β cells in the pancreatic islets, irregular islet architecture with intraislet ducts, and degenerative as well as hypertrophic changes in the individual β cells. As a rule, islets microdissected from these mice did not release insulin in response to glucose, theophylline, iodoacetamide, or chloromercuribenzene-p-sulphonic acid. The absence of secretory responses was not simply due to lack of insulin. Although the islet content of insulin was decreased in C57BL/KsJ-db/db mice, the remaining amount was severalfold larger than that released from stimulated islets of normal controls. Another mutation, db^2J, an allele of db with identical phenotypic expressions in the C57BL/KsJ strain, was studied on the genetic background C57BL/6J. In contrast to the severely diabetic C57BL/KsJ-db/db animals, the C57BL/6J-db^2J/db^2J mice were characterized by highly elevated serum insulin levels and only moderate hyperglycemia. Their endocrine pancreas was enlarged and showed an increased proportion of β cells. Like the islets of normal mice, those of C57BL/6J-db^2J/db^2J mice responded to glucose and chloromercuribenzene-p-sulphonic acid, the glucose-induced responses being potentiated by theophylline or iodoacetamide. C57BL/KsJ-db/db mice should provide a valuable model for studying defects in insulin secretion in relation to diabetes mellitus. Mice of the C57BL/6J strain offer a control material that may help to elucidate the dependence of the insulin secretory defect on the background genome.     

Alpha-pheromone-induced "shmooing" and gene regulation require white-opaque switching during Candida albicans mating

A 14-mer α-pheromone peptide of Candida albicans was chemically synthesized and used to analyze the role of white-opaque switching in the mating process. The α-pheromone peptide blocked cell multiplication and induced “shmooing” in a/a cells expressing the opaque-phase phenotype but not in a/a cells expressing the white-phase phenotype. The α-pheromone peptide induced these effects at 25°C but not at 37°C. An analysis of mating-associated gene expression revealed several categories of gene regulation, including (i) MTL-homozygous-specific, pheromone stimulated, switching-independent (CAG1 and STE4); (ii) mating type-specific, pheromone-induced, switching-independent (STE2); and (iii) pheromone-induced, switching-dependent (FIG1, KAR4, and HWP1). An analysis of switching-regulated genes revealed an additional category of opaque-phase-specific genes that are downregulated by α-pheromone only in a/a cells (OP4, SAP1, and SAP3). These results demonstrate that α-pheromone causes shmooing, the initial step in the mating process, only in a/a cells expressing the opaque phenotype and only at temperatures below that in the human host. These results further demonstrate that although some mating-associated genes are stimulated by the α-pheromone peptide in both white- and opaque-phase cells, others are stimulated only in opaque-phase cells, revealing a category of gene regulation unique to C. albicans in which α-pheromone induction requires the white-opaque transition. These results demonstrate that in C. albicans, the mating process and associated gene regulation must be examined within the context of white-opaque switching.     

Letter: Notes on "heat loss from a Newtonian animal"

Parker, Baker &; Smith (1972) have demonstrated mathematically that given the evolution of sexual reproduction, disruptive selection for the production of either many small gametes or a few large gametes may occur, resulting in a stable polymorphism of “sperm” and “egg” producers. Their model for the evolution of anisogamy requires only that zygote fitness (F) increase steeply with increases in zygote volume (V) (for Foc∝ V^x, x must be greater than 1·5) and that a sufficiently broad range of zygote productivity-size variants exist in the population (the higher the value of x, the broader the range needed). They suggest that anisogamy is almost universal in multicellular organisms but relatively rare in unicellular organisms because only for the former is an investment in extra gametic reserves at the expense of the number of gametes produced likely to be worthwhile in terms of increasing the survival probability of the zygote. In this note a graphical analysis and evidence from the anisogamous Protista will be presented concerning this hypothesis.     

Induction of "pore" formation in plant cell membranes by toluene

Treatment with aqueous toluene-ethanol has been shown to induce “pore” formation in plant cell membranes. The evidence is as follows: [List: see text]

While the principal experimental material was roots of Atriplex nummularia Lindl., the fact that similar results were also observed with leaves of Pisum sativum L. and with the alga Chlorella pyrenoidosa Chik. suggests that the phenomenon is general.

Although the phenomenon of pore induction is qualitatively similar to that in microorganisms, the pores induced appear to be smaller. It is proposed that induced leakage could be the basis for the development of simple and rapid methods for plant biochemical studies.

     

Expression of "Dehydrin-Like" Proteins in Embryos and Seedlings of Zizania palustris and Oryza sativa during Dehydration

Proteins inducible by dehydration and abscisic acid (ABA), termed dehydrins or RAB (Responsive to ABA) proteins, have been identified in a number of species and have been suggested to play a role in desiccation tolerance, particularly during seed development. Seeds (caryopses) of North American wild rice (Zizania palustris var interior [Fassett] Dore) are tolerant of dehydration to <10% moisture content (fresh weight basis) only under restricted dehydration and rehydration conditions. In comparison, seeds of paddy rice (Oryza sativa L.) readily tolerate desiccation to <5% water content. Expression of “dehydrin-like” proteins in Zizania and Oryza seedlings and embryos was examined to investigate the relationship between the presence of such proteins and desiccation tolerance. [³⁵S]Methionine labeling of newly synthesized proteins showed that seedlings (first leaf stage) of both Zizania and Oryza synthesized a novel “heat-stable” protein of apparent molecular weight = 20,000 when dehydrated to <75% of their initial fresh weight. ABA (100 micromolar) induced synthesis of a protein with similar electrophoretic mobility in both species. Western blots using antiserum raised against maize (Zea mays L.) dehydrin detected a protein band from dehydrated Zizania shoots and mature embryonic axes that comigrated with the labeled 20-kilodalton polypeptide. Northern blots using a cDNA for an ABA-responsive protein from Oryza (rab 16a) showed that both seedlings and excised embryonic axes of Zizania accumulated RNA similar in sequence to rab 16a in response to water loss. Zizania seedlings and embryonic axes were also capable of ABA accumulation during dehydration. The intolerance of Zizania seeds to dehydration at low temperature is apparently not due to an absence of dehydrin-like proteins or an inability to accumulate ABA.     

A Nonproteolytic "Trypsin-like" Enzyme: Purification and Properties of Arachain

By the use of the proteolytic substrates benzoyl-dl-arginine-p-nitroanilide and benzoyl-l-arginine ethyl ester the enzyme arachain has been purified 325-fold from acetone powders of ungerminated peanuts. The pH optimum for the hydrolysis of benzoyl-dl-arginine-p-nitroanilide was 8.1 in tris buffer, and for benzoyl-l-arginine ethyl ester was 7.5 using N - 2 - hydroxyethylpiperazine - N′ - 2 - ethanesulfonic acid buffer. The purest fraction showed one main band with one to three minor bands on disc gel electrophoresis. The major protein component had an S_20,w of 6.20. The energy of activation for the hydrolysis of benzoyl-dl-arginine-p-nitroanilide was calculated to be 16 kilocalories. The Michaelis constant for benzoyl-dl-arginine-p-nitroanilide was 10 micromolar and for benzoyl-l-arginine ethyl ester was 110 micromolar. The enzyme showed essentially no activity with casein, dimethyl casein, or bovine serum albumin as substrates. A large number of peptides were hydrolyzed by the enzyme, only l-leucyl-l-tyrosine being resistant of the peptides tested. The results suggest that arachain is not a “trypsin-like” protease but is a peptide hydrolase.     

Functional subsets of human T cells defined by "active" rosette formation

Experiments were conducted defining the possible basis for increased susceptibility of alloxan-treated and genetically diabetic C57Bl/KsJ mice to infections with Candida albicans. Alloxan monohydrate (175 mg/kg) produced a prolonged state of hyperglycemia, which persisted through 31 days. Parameters of immune responses varied depending upon the interval between alloxan administration and testing. In the period immediately following alloxan treatment (1–14 days), the numbers of lymphocytes in the thymus and spleen were reduced, the numbers of recoverable peritoneal macrophages were decreased, and the mice showed an increased susceptibility to intravenous infection with C. albicans. In contrast, splenic lymphocytes responded normally to stimulation with Con A, and in vitro phagocytosis of yeast cells by peritoneal macrophages was normal. Also, in vivo production of such lymphokines as migration inhibitory factor (MIF) and macrophage activating factor (MAF), as well as delayed hypersensitivity footpad responses, was generally within the normal range. In the later phase of alloxan diabetes (21–28 days) after administration of alloxan, lymphoid cellularity recovered progressively and the numbers of recoverable peritoneal macrophages were normal. However, these mice still showed an increased susceptibility to C. albicans infection. Genetically diabetic mice (C57Bl/KsJ, db/db) were abnormal in virtually all the assays involving cell-mediated immunity. The numbers of lymphocytes and peritoneal macrophages were markedly decreased, lymphoid cells responded poorly to Con A, and the phagocytosis of yeast cells by macrophages was depressed. The in vivo production of lymphokines and footpad responses of the delayed-type hypersensitivity were depressed. In addition, these mice were highly susceptible to intravenous infection with C. albicans.