Effect of Rec− Mutations on the Activity of Colicinogenic Factors

The effect of two Rec(-) mutations (AB2463 and JC1553) on the ability of a cell to accept, maintain, and express the colicinogenic factors ColE(1), ColE(2), and ColV was examined in Escherichia coli. These mutations had no observable effect on the colicinogenic properties of the ColV factor, but prevented the spontaneous and induced production of colicins E(1) and E(2) which are determined by the ColE(1) and ColE(2) factors, respectively. The two Rec(-) mutations had no apparent effect on the ability of the cells to acquire, maintain, or transfer the ColE(1) and ColE(2) factors. These mutations did not affect the expression of immunity by any of the three Col factors. ColE(1) and ColE(2) were also shown to be indirectly induced by mating F(-) cells carrying these Col factors with ultraviolet-irradiated, non-colicinogenic, Hfr and F(+) cells. Indirect induction of colicin production occurred when either an irradiated F(+) Rec(+) or F(+) Rec(-) strain was employed as the donor strain.     

Genetic exchange between Escherichia coli strains in the mouse intestine

Germ-free mice contaminated with selected Escherichia coli strains were used for experiments designed to demonstrate gene transfer and recombinant formation in vivo. The well-characterized conjugation system of E. coli K-12 was examined in these experiments. Contamination of germ-free mice with a polyauxotrophic F(-) strain followed by the addition of isogenic Hfr, F', or F(+) strains resulted in the appearance of all recombinant classes at frequencies that would be expected from an in vitro mating experiment. Inheritance of unselected donor markers occurred at frequencies that were dependent on linkage relationships established in experiments in vitro. The presence of Lactobacillus had no influence on gene transfer and recombinant formation in an F' x F(-) in vivo mating. The R factor ROR-1 was transferred from E. coli strain M7-18 to an E. coli F(-) strain in the mouse intestine.     

Role of Pili in Bacterial Conjugation

We describe techniques for isolating individual pairs of mating Escherichia coli and observing them under the light microscope. Some pairs achieved close cell-to-cell contact, whereas others remained loosely connected by invisible connections which may be F pili. After 30 min of mating, the pairs were separated and allowed to grow into clones. That many exconjugants derived from "loose"-mating pairs produced recombinants suggests that F pili are involved in the transfer of genetic material. The frequency of formation of recombinants from "close"-mating pairs, however, was significantly higher than that from loose-mating pairs, indicating that a close cell-to-cell contact facilitates chromosome transfer. Death rates of exconjugants from close pairs were also higher than those from loose pairs. Hfr x F(-) matings produced higher death rates than F(+) x F(-) matings. Male cells were found capable of transferring genetic markers to two F(-) cells simultaneously. We conclude that F pili play at least three roles in mating: (i) they initiate contacts between mating pairs; (ii) they facilitate the transfer of genetic material; and (iii) they draw mating cells into a close contact which increases the fertility of the union.     

Inhibition of Replication of an F′lac Episome in Hfr Cells of Escherichia coli

Hfr strains of Escherichia coli K-12 were found capable of accepting a F'lac episome during mating, with a frequency approximating that of F(-) strains. However, the F'lac episome was unable to replicate in the Hfr cells, and was diluted out during the growth of the culture. The lac(+) gene of the episome can be "rescued" by recombination into the host chromosome, as shown by the appearance of variegated recombinant colonies on a lactose-fermentation indicator medium. In recA Hfr strains, however, no lac(+) offspring were obtained in crosses with F'lac donors. The induced synthesis of beta-galactosidase in F'lac(+) x Hfr zygotes was studied. Rates of enzyme synthesis were approximately constant with respect to time as expected from unilinear inheritance of the F'lac episome. However, the rate of synthesis eventually increased, presumably due to integration of the lac(+) gene in some of the zygotes. In F'lac(+) x recA Hfr zygotes the rate of beta-galactosidase synthesis remained constant with respect to time, as expected.     

Interaction between colicinogenic factor V and the integrated F factor in an Hfr strain of Escherichia coli

Kahn, Phyllis L. (Princeton University, Princeton, N.J.), and Donald R. Helinski. Interaction between colicinogenic factor V and the integrated F factor in an Hfr strain of Escherichia coli. J. Bacteriol. 90:1276-1282. 1965.-The production of colicin V by strains of Escherichia coli is determined by a colicinogenic factor, colV. The colV factor possesses a genetic determinant of fertility, F(v). V(+)F(v) (+) cells are characteristically susceptible to a male-specific phage, mu, and able to transfer the colV factor and chromosomal markers to recipient cells. The present work describes an interaction of the colV factor with the chromosome of the Hfr strain, HfrH. A colV-containing HfrH strain, designated HfrHV(+)F(v) (+)(l), was isolated and shown to be insensitive to phage mu and impaired in its fertility properties. Loss of the colV factor by this strain, either spontaneous or induced by acridine orange, resulted in a further 10(3)- or 10(4)-fold loss in fertility. This additional loss of fertility was restored by reinfection of these strains with the colV factor. The colV interaction with the HfrH chromosome also can result in defects in the fertility properties of the colV factor. Altered colV factors were found in recombinants isolated from a cross between the HfrHV(+)F(v) (+)(l) strain and F(-) recipients. It is postulated that in the HfrHV(+)F(v) (+)(l) strain an interaction of the colV episome with the integrated F region of the chromosome occurs, with a resulting modification of the fertility properties of the HfrH strain. This interaction can also result in a defect in certain properties of the colV factor.     

Modification to the capsid of the adenovirus vector that enhances dendritic cell infection and transgene-specific cellular immune responses

Adenovirus (Ad) gene transfer vectors can be used to transfer and express antigens and function as strong adjuvants and thus are useful platforms for the development of genetic vaccines. Based on the hypothesis that Ad vectors with enhanced infectibility of dendritic cells (DC) may be able to evoke enhanced immune responses against antigens encoded by the vector in vivo, the present study analyzes the vaccine potential of an Ad vector expressing beta-galactosidase as a model antigen and genetically modified with RGD on the fiber knob [AdZ.F(RGD)] to more selectively infect DC and consequently enhance immunity against the beta-galactosidase antigen. Infection of murine DC in vitro with AdZ.F(RGD) showed an eightfold-increased transgene expression following infection compared to AdZ (also expressing beta-galactosidase, but with a wild-type capsid). Binding, cellular uptake, and trafficking in DC were also increased with AdZ.F(RGD) compared to AdZ. To determine whether AdZ.F(RGD) could evoke enhanced immune responses to beta-galactosidase in vivo, C57BL/6 mice were immunized with AdZ.F(RGD) or AdZ subcutaneously via the footpad. Humoral responses with both vectors were comparable, with similar anti-beta-galactosidase antibody levels following vector administration. However, cellular responses to beta-galactosidase were significantly enhanced, with the frequency of CD4(+) as well as the CD8(+) beta-galactosidase-specific gamma interferon response in cells isolated from the draining lymph nodes increased following immunization with AdZ.F(RGD) compared to Ad.Z (P < 0.01). Importantly, this enhanced cellular immune response of the AdZ.F(RGD) vector was sufficient to evoke enhanced inhibition of the growth of preexisting tumors expressing beta-galactosidase: BALB/c mice implanted with the CT26 syngeneic beta-galactosidase-expressing colon carcinoma cell line and subsequently immunized with AdZ.F(RGD) showed decreased tumor growth and improved survival compared to mice immunized with AdZ. These data demonstrate that addition of an RGD motif to the Ad fiber knob increases the infectibility of DC and leads to enhanced cellular immune responses to the Ad-transferred transgene, suggesting that the RGD capsid modification may be useful in developing Ad-based vaccines.     

Isolation and Characterization of a Recombination-Deficient Hfr Strain

The isolation of a rec(-) Hfr strain of Escherichia coli K-12 is described. The method used consisted of mating AB2463 F(-) Rec(-) His(-) Lac(-) with P4X6 Hfr Rec(+) His(+) Lac(+), selecting Rec(-) His(-) Lac(+) recombinants, and searching for Hfr strains. One Hfr rec(-) strain, no. 12, was used as donor in crosses with Rec(+) and Rec(-) recipients. Crosses with Rec(+) recipients are fertile, and those with Rec(-) recipients are almost infertile, the frequency of recombinants being 10(-2) to 10(-3) that found with Rec(+) recipients. The Rec(-) mutant marker is transfered to and integrated into Rec(+) recipients. Zygotic induction of prophage lambda is observed in crosses between two Rec(-) strains. In crosses of F(-) Rec(-) with Hfr Rec(-), the gradient of integration frequencies for markers progressively more distant from the origin is steeper than in the Rec(+) x Rec(-) or the Rec(-) x Rec(+) crosses.     

Effect of Zn2+ on bacterial conjugation: inhibition of mating pair formation

Zn(2+) at 10(-3)m has been found to block the formation of mating pairs between Hfr and F(-) strains of Escherichia coli as observed both by light microscopy and by Coulter counter measurements. Kinetic studies show that Zn(2+) reduces the fertility of the male and that its effect disappears within 2 min after Zn(2+) has been removed from the medium. Short treatments of female cells with Zn(2+) have no detectable effect on their ability to form mating pairs. Later steps in the mating process such as mobilization of the male chromosome, transfer of the chromosome to the female, or its integration into the female chromosome seem not to be affected by 10(-3)m Zn(2+).     

Deoxyribonucleic Acid Transferred from Ultraviolet-Irradiated Excision-Defective Hfr Cells of Escherichia coli K-12

Deoxyribonucleic acid (DNA) transfer from (3)H-thymine-labeled Hfr cells has been measured by determining the amount of radioactivity remaining after selective lysis of the donor cells in the mating mixture. DNA transfer was less effectively reduced by ultraviolet irradiation of excision-defective Hfr cells than was the yield of recombinants. The buoyant density of DNA transferred from unirradiated and irradiated Hfr cells was equivalent to that of double-stranded DNA. Mating-dependent DNA synthesis in the recipient has been measured by mating Hfr cells deficient in thymidine kinase with irradiated thymine-requiring F(-) cells in the presence of (3)H-thymine. The extent of such DNA synthesis approximated the amount of DNA transferred from unirradiated donors. Neither DNA transfer nor mating-dependent DNA synthesis could be reliably measured when both parents were irradiated. It is proposed that transferred Hfr DNA is replicated in the recipient and that this replication still occurs when the Hfr DNA contains dimers.     

Effect of Bacillus subtilis BsuM restriction-modification on plasmid transfer by polyethylene glycol-induced protoplast fusion

Polyethylene glycol (PEG)-induced cell fusion is a promising method to transfer larger DNA from one cell to another than conventional genetic DNA transfer systems. The laboratory strain Bacillus subtilis 168 contains a restriction (R) and modification (M) system, BsuM, which recognizes the sequence 5'-CTCGAG-3'. To study whether the BsuM system affects DNA transfer by the PEG-induced cell fusion between R(+)M(+) and R(-)M(-) strains, we examined transfer of plasmids pHV33 and pLS32neo carrying no and eight BsuM sites, respectively. It was shown that although the transfer of pLS32neo but not pHV33 from the R(-)M(-) to R(+)M(+) cells was severely restricted, significant levels of transfer of both plasmids from the R(+)M(+) to R(-)M(-) cells were observed. The latter result shows that the chromosomal DNA in the R(-)M(-) cell used as the recipient partially survived restriction from the donor R(+)M(+) cell, indicating that the BsuM R(-)M(-) strain is useful as a host for accepting DNA from cells carrying a restriction system(s). Two such examples were manifested for plasmid transfer from Bacillus circulans and Bacillus stearothermophilus strains to a BsuM-deficient mutant, B. subtilis RM125.     

Ultraviolet-sensitive Targets in the Enzyme-synthesizing Apparatus of Escherichia coli

Inhibition by ultraviolet light of beta-galactosidase and alkaline phosphatase synthesis was investigated in both ultraviolet (UV)-sensitive and UV-resistant (wild-type) Escherichia coli, with the objective of determining the sensitivity of various targets. Kinetics of enzyme formation by unmated bacteria and in mating systems, in which the donor provided the specific genetic material and the recipient the cytoplasm, permit the following conclusions regarding the sensitivity of various targets. Catabolite repression resulting from UV damage causes most of the inhibition of beta-galactosidase formation. When it is largely eliminated by a step-down in nutrition, the principal target in UV-sensitive bacteria appears to be the structural gene (lacZ(+)), but damage to the cytoplasm is also important. Transitory inhibition by inactivation of messenger ribonucleic acid is also observed. In wild-type bacteria, repair reduces the importance of lesions in deoxyribonucleic acid sufficiently that cytoplasmic damage appears to be at least as important. Repair occurs within 10 min, as shown by recovery of enzyme-synthesizing ability. Caffeine and proflavine prevent recovery. Newly mated bacteria respond to irradiation very differently than do unmated bacteria. The beta-galactosidase or alkaline phosphatase structural gene (lacZ(+) or phoP(+)) is much more inhibited after it is transferred than it is in unmated bacteria. This sensitivity seems to depend on a sensitive state of the injected material, rather than on a different physiological condition of the entire zygote. Irradiation of recipient uvr(+) bacteria much more strongly inhibited expression of injected genes than if the F(-) was uvr(s). Studies on mating systems are not very useful for learning about the function of unmated bacteria.     

Effect of point mutations in the lac promoter on transient and severe catabolite repression of the lac operon of Escherichia coli

1. Experiments were devised to show whether the point mutations L8 and L29 in the lac promoter alleviate transient repression. 2. Several recombinants were picked from matings between a single F(-)p(+) strain and Hfr strains carrying mutations L8 and L29. All of the 19 p(-) recombinants tested proved to suffer no transient repression, whereas all of the eight p(+) recombinants tested suffered prolonged transient repression. 3. A diploid strain was constructed in which more than 90% of the thiogalactoside transacetylase is synthesized from the episome with a wild-type lac promoter, whereas 100% of the beta-galactosidase is synthesized from the chromosome with a promoter carrying mutation L8. In this diploid the synthesis of thiogalactoside transacetylase suffered transient repression but the synthesis of beta-galactosidase did not. 4. Exactly similar results were obtained with a diploid strain in which the chromosomal promoter carried mutation L29. 5. The same diploid strains were used in experiments to show whether mutations L8 and L29 alleviate the severe catabolite repression caused by growth in glucose plus gluconate. In both strains glucose+gluconate repressed the synthesis of beta-galactosidase much less than the synthesis of thiogalactoside transacetylase. 6. These and previously reported results can be explained by assuming (a) that both mutations L8 and L29 render the lac promoter partially, but not completely, insensitive to catabolite repression, and (b) that transient repression is an exceptionally severe form of catabolite repression.     

The activity of immunoregulatory T cells mediating active tolerance is potentiated in nonobese diabetic mice by an IL-4-based retroviral gene therapy

Splenocytes from nonobese diabetic mice overexpressing murine IL (mIL)-4 upon recombinant retrovirus infection lose their capacity to transfer diabetes to nonobese diabetic-scid recipients. Diabetes appeared in 0-20% of mice injected with mIL-4-transduced cells vs 80-100% of controls injected with beta-galactosidase-transduced cells. Protected mice showed a majority of islets (60%) presenting with noninvasive peri-insulitis at variance with beta-galactosidase controls that exhibited invasive/destructive insulitis. Importantly, in all recipients, the transduced proteins were detected within islet infiltrates. Infiltrating lymphocytes from recipients of mIL-4-transduced cells produced high levels of mIL-4, as assessed by ELISA. In recipients of beta-galactosidase-transduced cells, approximately 60% of TCRalphabeta(+) islet-infiltrating cells expressed beta-galactosidase, as assessed by flow cytometry. The protection from disease transfer is due to a direct effect of mIL-4 gene therapy on immunoregulatory T cells rather than on diabetogenic cells. mIL-4-transduced purified CD62L(-) effector cells or transgenic BDC2.5 diabetogenic T cells still transferred disease efficiently. Conversely, mIL-4 transduction up-regulated the capacity of purified immunoregulatory CD62L(+) cells to inhibit disease transfer. These data open new perspectives for gene therapy in insulin-dependent diabetes using T cells devoid of any intrinsic diabetogenic potential.     

An active type IV secretion system encoded by the F plasmid sensitizes Escherichia coli to bile salts

F(+) strains of Escherichia coli infected with donor-specific bacteriophage such as M13 are sensitive to bile salts. We show here that this sensitivity has two components. The first derives from secretion of bacteriophage particles through the cell envelope, but the second can be attributed to expression of the F genes required for the formation of conjugative (F) pili. The latter component was manifested as reduced or no growth of an F(+) strain in liquid medium containing bile salts at concentrations that had little or no effect on the isogenic F(-) strain or as a reduced plating efficiency of the F(+) strain on solid media; at 2% bile salts, plating efficiency was reduced 10(4)-fold. Strains with F or F-like R factors were consistently more sensitive to bile salts than isogenic, plasmid-free strains, but the quantitative effect of bile salts depended on both the plasmid and the strain. Sensitivity also depended on the bile salt, with conjugated bile salts (glycocholate and taurocholate) being less active than unconjugated bile salts (deoxycholate and cholate). F(+) cells were also more sensitive to sodium dodecyl sulfate than otherwise isogenic F(-) cells, suggesting a selectivity for amphipathic anions. A mutation in any but one F tra gene required for the assembly of F pili, including the traA gene encoding F pilin, substantially restored bile salt resistance, suggesting that bile salt sensitivity requires an active system for F pilin secretion. The exception was traW. A traW mutant was 100-fold more sensitive to cholate than the tra(+) strain but only marginally more sensitive to taurocholate or glycocholate. Bile salt sensitivity could not be attributed to a generalized change in the surface permeability of F(+) cells, as judged by the effects of hydrophilic and hydrophobic antibiotics and by leakage of periplasmic beta-lactamase into the medium.     

Plasmid-associated transfer of tetracycline resistance in Bacteroides ruminicola

Tetracycline resistance was transferred at frequencies between 10(-7) and 10(-6) per recipient cell in anaerobic matings between two strains of the strictly anaerobic rumen bacterium Bacteroides ruminicola. The donor strain, 223/M2/7, was a multiple-plasmid-bearing tetracycline-resistant strain from the ovine rumen, and the recipient, F101, was a rifampin-resistant mutant of B14, a bovine strain belonging to B. ruminicola subsp. brevis. Resistance transfer could occur in the presence of DNase, but not in dummy mating mixtures in which filtrate from a donor culture replaced donor cells. Acquisition of tetracycline resistance by the recipient was accompanied by the appearance of a 19.5-kilobase pair plasmid (designated pRRI4) which was homologous with a plasmid of similar size and restriction pattern present in the donor strain. A transconjugant (F115) carrying pRRI4 was also able to act as a donor of tetracycline resistance and plasmid DNA in matings with another recipient. Derivatives of F115 that had spontaneously lost tetracycline resistance lacked detectable plasmid DNA. It is concluded that pRRI4 mediated the transfer of tetracycline resistance. Transfer of resistance was not detectably enhanced by pregrowth of the donor in medium containing tetracycline. Transfer of tetracycline resistance was not detected from 223/M2/7 to a strain, 23 belonging to B. ruminicola subsp. ruminicola.     

Plasmid-associated transfer of tetracycline resistance in Bacteroides ruminicola.

Tetracycline resistance was transferred at frequencies between 10(-7) and 10(-6) per recipient cell in anaerobic matings between two strains of the strictly anaerobic rumen bacterium Bacteroides ruminicola. The donor strain, 223/M2/7, was a multiple-plasmid-bearing tetracycline-resistant strain from the ovine rumen, and the recipient, F101, was a rifampin-resistant mutant of B14, a bovine strain belonging to B. ruminicola subsp. brevis. Resistance transfer could occur in the presence of DNase, but not in dummy mating mixtures in which filtrate from a donor culture replaced donor cells. Acquisition of tetracycline resistance by the recipient was accompanied by the appearance of a 19.5-kilobase pair plasmid (designated pRRI4) which was homologous with a plasmid of similar size and restriction pattern present in the donor strain. A transconjugant (F115) carrying pRRI4 was also able to act as a donor of tetracycline resistance and plasmid DNA in matings with another recipient. Derivatives of F115 that had spontaneously lost tetracycline resistance lacked detectable plasmid DNA. It is concluded that pRRI4 mediated the transfer of tetracycline resistance. Transfer of resistance was not detectably enhanced by pregrowth of the donor in medium containing tetracycline. Transfer of tetracycline resistance was not detected from 223/M2/7 to a strain, 23 belonging to B. ruminicola subsp. ruminicola.     

Molecular Studies on Entry Exclusion in Escherichia coli Minicells

Minicells produced by abnormal cell division in a strain of Escherichia coli (K-12) have been employed here to investigate the phenomenon of "entry exclusion." When purified minicells from strains containing F' or R factors, or both, are mated with radioactive thymidine-labeled Hfr or R(+) donors, the recipient minicells can be conveniently separated from normal-sized donors following mating, and the products of conjugation can be analyzed in the absence of donors and of further growth of the recipients. Transmissible plasmids or episomes are transferred less efficiently to purified minicells derived from strains carrying similar or related elements than to strains without them. Measurement of deoxyribonucleic acid (DNA) degradation and determination of weight-average molecular weights following transfer indicate that degradation of transferred DNA or transfer of smaller pieces cannot account for the comparative reduction in transfer to entry-excluding recipients. Therefore, we conclude that entry exclusion operates to prevent the physical entry of DNA into recipients expressing the exclusion phenotype. The R-produced repressor (product of the drd(+) gene), which represses fertility (i.e., ability to act as donor), reduces exclusion mediated by R or F factor, or both, in matings between strains carrying homologous elements. Furthermore, the data suggest that the presence of the F pilus or F-like R pilus on recipient cells ensures maximum expression of the exclusion phenotype but is not essential for its expression. In contrast to previous suggestions, we found no evidence for a reduction of entry exclusion attributable to the DNA temperature-sensitive chromosomal mutation dnaB(TS).     

Isolation of the nonviable cells produced during normal growth of recombination-deficient strains of Escherichia coli K-12

During normal growth, cultures of recombination-deficient (Rec(-)) strains contain a population of cells that do not form colonies. Such cells are not present in a culture of an isogenic Rec(+) strain. We present a procedure for isolating and studying this defective population of cells. Exposure of a growing Rec(-) or Rec(+) culture to low levels of penicillin causes the dividing cells to elongate. The size of the nonviable cells present in the Rec(-) cultures is unaffected. The nonviable cells are then separated from the elongated cells by velocity sedimentation. This isolation technique provides a convenient way of analyzing the composition, biosynthetic capacity, and enzymatic function of the nonviable cells before isolation. In this paper we present data showing that before fractionation the nonviable cells in the Rec(-) culture are defective in their ability to synthesize beta-galactosidase, whereas the Rec(-) viable cells behave like the Rec(+) cells in this regard. This observation confirms the existence of at least two classes of cells in liquid cultures of Rec(-) strains grown under normal conditions. That class of cells which is unable to synthesize beta-galactosidase is the same class that cannot form colonies when plated on solid medium.     

Effect of Thymine-5-Bromouracil Substitution on F Pili

The effect of thymine-5-bromouracil substitution on the regeneration and length of F pili produced by an F(+)Lac(+)/Lac(-)Thy(-) strain of Escherichia coli was studied by electron microscopy. When 5-bromouracil (5BU) incorporation into deoxyribonucleic acid (DNA) was maximal, the modal length of the pilus doubled and the number of pili per cell was approximately 50% that of thymine-grown cells. The ability of 5BU-grown cells to form mating pairs and to be infected by ribonucleic acid (R17) and DNA (M13) male-specific phages was also reduced by approximately 50%. Loss of function was not due to loss of sex factor as 5BU cells retained a sex factor that was susceptible to curing by acridine orange. Elongation of pili on 5BU-grown cells was more sensitive to irradiation at 253.7 nm than on thymine-grown cells, suggesting that DNA is the sensitive target.     

Functional specializations of intestinal dendritic cell and macrophage subsets that control Th17 and regulatory T cell responses are dependent on the T cell/APC ratio, source of mouse strain, and regional localization

Although several subsets of intestinal APCs have been described, there has been no systematic evaluation of their phenotypes, functions, and regional localization to date. In this article, we used 10-color flow cytometry to define the major APC subsets in the small and large intestine lamina propria. Lamina propria APCs could be subdivided into CD11c(+)CD11b(-), CD11c(+)CD11b(+), and CD11c(dull)CD11b(+) subsets. CD11c(+)CD11b(-) cells were largely CD103(+)F4/80(-) dendritic cells (DCs), whereas the CD11c(+)CD11b(+) subset comprised CD11c(+)CD11b(+)CD103(+)F4/80(-) DCs and CD11c(+)CD11b(+)CD103(-)F4/80(+) macrophage-like cells. The majority of CD11c(dull)CD11b(+) cells were CD103(-)F4/80(+) macrophages. Although macrophages were more efficient at inducing Foxp3(+) regulatory T (T(reg)) cells than DCs, at higher T cell/APC ratios, all of the DC subsets efficiently induced Foxp3(+) T(reg) cells. In contrast, only CD11c(+)CD11b(+)CD103(+) DCs efficiently induced Th17 cells. Consistent with this, the regional distribution of CD11c(+)CD11b(+)CD103(+) DCs correlated with that of Th17 cells, with duodenum > jejunum > ileum > colon. Conversely, CD11c(+)CD11b(-)CD103(+) DCs, macrophages, and Foxp3(+) T(reg) cells were most abundant in the colon and scarce in the duodenum. Importantly, however, the ability of DC and macrophage subsets to induce Foxp3(+) T(reg) cells versus Th17 cells was strikingly dependent on the source of the mouse strain. Thus, DCs from C57BL/6 mice from Charles River Laboratories (that have segmented filamentous bacteria, which induce robust levels of Th17 cells in situ) were more efficient at inducing Th17 cells and less efficient at inducing Foxp3(+) T(reg) cells than DCs from B6 mice from The Jackson Laboratory. Thus, the functional specializations of APC subsets in the intestine are dependent on the T cell/APC ratio, regional localization, and source of the mouse strain.