Commensal Bacteria Impact on Intestinal Toll-like Receptor Signaling in Salmonella-Challenged Gnotobiotic Piglets

Gnotobiotic (GN) animals with simple and defined microbiota can help to elucidate host-pathogen interferences. Hysterectomy-derived germ-free (GF) minipigs were associated at 4 and 24 h post-hysterectomy with porcine commensal mucinolytic Bifidobacterium boum RP36 (RP36) strain or non-mucinolytic strain RP37 (RP37) or at 4 h post-hysterectomy with Lactobacillus amylovorus (LA). One-week-old GN minipigs were infected with Salmonella Typhimurium LT2 strain (LT2). We monitored histological changes in the ileum, mRNA expression of Toll-like receptors (TLRs) 2, 4, and 9 and their related molecules lipopolysaccharide-binding protein (LBP), coreceptors MD-2 and CD14, adaptor proteins MyD88 and TRIF, and receptor for advanced glycation end products (RAGE) in the ileum and colon. LT2 significantly induced expression of TLR2, TLR4, MyD88, LBP, MD-2, and CD14 in the ileum and TLR4, MyD88, TRIF, LBP, and CD14 in the colon. The LT2 infection also significantly increased plasmatic levels of inflammatory markers interleukin (IL)-6 and IL-12/23p40. The previous colonization with RP37 alleviated damage of the ileum caused by the Salmonella infection, and RP37 and LA downregulated plasmatic levels of IL-6. A defined oligo-microbiota composed of bacterial species with selected properties should probably be more effective in downregulating inflammatory response than single bacteria.

Release of HMGB1 and Toll-like Receptors 2, 4, and 9 Signaling Are Modulated by Bifidobacterium animalis subsp. lactis BB-12 and Salmonella Typhimurium in a Gnotobiotic Piglet Model of Preterm Infants

Gnotobiotic (GN) animals with defined microbiota allow us to study host-microbiota and microbiota-microbiota interferences. Preterm germ-free (GF) piglets were mono-associated with probiotic Bifidobacterium animalis subsp. lactis BB-12 (BB12) to ameliorate/prevent the consequences of infection with the Salmonella Typhimurium strain LT2 (LT2). Goblet cell density; expression of Toll-like receptors (TLRs) 2, 4, and 9; high mobility group box 1 (HMGB1); interleukin (IL)-6; and IL-12/23p40 were analyzed to evaluate the possible modulatory effect of BB12. BB12 prevented an LT2-induced decrease of goblet cell density in the colon. TLRs signaling modified by LT2 was not influenced by the previous association with BB12. The expression of HMGB1, IL-6, and IL12/23p40 in the jejunum, ileum, and colon and their levels in plasma were all decreased by BB12, but these changes were not statistically significant. In the colon, differences in HMGB1 distribution between the GF and LT2 piglet groups were observed. In conclusion, the mono-association of GF piglets with BB12 prior to LT2 infection partially ameliorated the inflammatory response to LT2 infection.

Condensed Clustered Iron Oxides for Ultrahigh Photothermal Conversion and In Vivo Multimodal Imaging

Magnetic iron oxide nanocrystals (MIONs) are established as potent theranostic nanoplatforms due to their biocompatibility and the multifunctionality of their spin-active atomic framework. Recent insights have also unveiled their attractive near-infrared photothermal properties, which are, however, limited by their low near-infrared absorbance, resulting in noncompetitive photothermal conversion efficiencies (PCEs). Herein, we report on the dramatically improved photothermal conversion of condensed clustered MIONs, reaching an ultrahigh PCE of 71% at 808 nm, surpassing the so-far MION-based photothermal agents and even benchmark near-infrared photothermal nanomaterials. Moreover, their surface passivation is achieved through a simple self-assembly process, securing high colloidal stability and structural integrity in complex biological media. The bifunctional polymeric canopy simultaneously provided binding sites for anchoring additional cargo, such as a strong near-infrared-absorbing and fluorescent dye, enabling in vivo optical and photoacoustic imaging in deep tissues, while the iron oxide core ensures detection by magnetic resonance imaging. In vitro studies also highlighted a synergy-amplified photothermal effect that significantly reduces the viability of A549 cancer cells upon 808 nm laser irradiation. Integration of such-previously elusive-photophysical properties with simple and cost-effective nanoengineering through self-assembly represents a significant step toward sophisticated nanotheranostics, with great potential in the field of nanomedicine.

The Differential Effect of Carbon Dots on Gene Expression and DNA Methylation of Human Embryonic Lung Fibroblasts as a Function of Surface Charge and Dose

This study presents a toxicological evaluation of two types of carbon dots (CD), similar in size (<10 nm) but differing in surface charge. Whole-genome mRNA and miRNA expression (RNAseq), as well as gene-specific DNA methylation changes, were analyzed in human embryonic lung fibroblasts (HEL 12469) after 4 h and 24 h exposure to concentrations of 10 and 50 µg/mL (for positive charged CD; pCD) or 10 and 100 µg/mL (for negative charged CD, nCD). The results showed a distinct response for the tested nanomaterials (NMs). The exposure to pCD induced the expression of a substantially lower number of mRNAs than those to nCD, with few commonly differentially expressed genes between the two CDs. For both CDs, the number of deregulated mRNAs increased with the dose and exposure time. The pathway analysis revealed a deregulation of processes associated with immune response, tumorigenesis and cell cycle regulation, after exposure to pCD. For nCD treatment, pathways relating to cell proliferation, apoptosis, oxidative stress, gene expression, and cycle regulation were detected. The expression of miRNAs followed a similar pattern: more pronounced changes after nCD exposure and few commonly differentially expressed miRNAs between the two CDs. For both CDs the pathway analysis based on miRNA-mRNA interactions, showed a deregulation of cancer-related pathways, immune processes and processes involved in extracellular matrix interactions. DNA methylation was not affected by exposure to any of the two CDs. In summary, although the tested CDs induced distinct responses on the level of mRNA and miRNA expression, pathway analyses revealed a potential common biological impact of both NMs independent of their surface charge.

The Effect of Rhodamine-Derived Superparamagnetic Maghemite Nanoparticles on the Motility of Human Mesenchymal Stem Cells and Mouse Embryonic Fibroblast Cells

Nanoparticles have become popular in life sciences in the last few years. They have been produced in many variants and have recently been used in both biological experiments and in clinical applications. Due to concerns over nanomaterial risks, there has been a dramatic increase in investigations focused on safety research. The aim of this paper is to present the advanced testing of rhodamine-derived superparamagnetic maghemite nanoparticles (SAMN-R), which are used for their nontoxicity, biocompatibility, biodegradability, and magnetic properties. Recent results were expanded upon from the basic cytotoxic tests to evaluate cell proliferation and migration potential. Two cell types were used for the cell proliferation and tracking study: mouse embryonic fibroblast cells (3T3) and human mesenchymal stem cells (hMSCs). Advanced microscopic methods allowed for the precise quantification of the function of both cell types. This study has demonstrated that a dose of nanoparticles lower than 20 µg·cm⁻² per area of the dish does not negatively affect the cells’ morphology, migration, cytoskeletal function, proliferation, potential for wound healing, and single-cell migration in comparison to standard CellTracker™ Green CMFDA (5-chloromethylfluorescein diacetate). A higher dose of nanoparticles could be a potential risk for cytoskeletal folding and detachment of the cells from the solid extracellular matrix.

Comparison of HLA-G and MMP transcription in human tumor cell lines

HLA-G antigens and matrix metalloproteinases (MMPs) expressed in various tumors are involved in tumor growth and metastasis. In this study, we investigated if correlation between HLA-G and MMP expression exists in different cell lines. We examined MMP transcription in two choriocarcinoma cell lines: JEG-3 (HLA-G positive) and JAR (HLA-G negative). We discovered that both cell lines express a similar panel of MMPs; except for MMP12. Transcript MMP12 was exclusively detected in HLA-G expressing JEG-3 cells but not in HLA-G deficient JAR cells. We observed HLA-G expression but no MMP12 transcription following 5-aza-2´-deoxycytidine (AZA) treatment of JAR cells. We then investigated HLA-G and MMP transcription in several human leukaemia cell lines. Leukaemia cells (lacking HLA-G expression) were converted to their HLA-G positive counterparts by AZA-treatment or by HLA-G transfection. It was found no correlation between HLA-G and MMP transcription in any examined leukaemia cell lines. The up-regulation of some MMPs and tissue inhibitors of matrix metalloproteinases (TIMPs) was observed following AZA-treatment.

Magnetic resonance cholangiopancreatography (MRCP) using new negative per-oral contrast agent based on superparamagnetic iron oxide nanoparticles for extrahepatic biliary duct visualization in liver cirrhosis

BACKGROUND AND AIMS

Magnetic resonance cholangiopancreatography (MRCP) is often used for imaging of the biliary tree and is required by surgeons before liver transplantation. Advanced liver cirrhosis and ascites in patients however present diagnostic problems for MRCP. The aim of this study was to find out if the use of our negative per-oral contrast agent containing superparamagnetic iron oxide nanoparticles (SPIO) in MRCP is helpful for imaging of hepatobiliary tree in patients with liver cirrhosis.

METHODS

Forty patients with liver cirrhosis were examined on a 1.5 T MR unit using standard MRCP protocol. Twenty patients (group A) underwent MRCP after administration of per-oral SPIO contrast agent 30 min before examination. In group B, twenty patients were examined without per-oral bowel preparation. Ascites was present in eleven patients from group A and in thirteen patients in group B. Four radiologists analyzed MR images for visibility and delineation of the biliary tree. χ² tests were used for comparison of the visibility of intrahepatic and extrahepatic biliary ducts in patients with and without ascites.

RESULTS

Better extrahepatic biliary duct visualization and visibility of extraluminal pathologies in patients with ascites was proved after administration of SPIO contrast agent. No statistically significant difference between group A and B was found for visualization of extrahepatic biliary ducts in patients without ascites. Delineation of intrahepatic biliary ducts was independent on bowel preparation.

CONCLUSIONS

Application of our negative per-oral SPIO contrast agent before MRCP improves the visualization of extrahepatic biliary ducts in patients with ascites which is helpful during the liver surgery, mainly in liver transplantation.

In vitro cytotoxicity analysis of doxorubicin-loaded/superparamagnetic iron oxide colloidal nanoassemblies on MCF7 and NIH3T3 cell lines

One of the promising strategies for improvement of cancer treatment is based on magnetic drug delivery systems, thus avoiding side effects of standard chemotherapies. Superparamagnetic iron oxide (SPIO) nanoparticles have ideal properties to become a targeted magnetic drug delivery contrast probes, named theranostics. We worked with SPIO condensed colloidal nanocrystal clusters (MagAlg) prepared through a new soft biomineralization route in the presence of alginate as the polymeric shell and loaded with doxorubicin (DOX). The aim of this work was to study the in vitro cytotoxicity of these new MagAlg-DOX systems on mouse fibroblast and breast carcinoma cell lines. For proper analysis and understanding of cell behavior after administration of MagAlg-DOX compared with free DOX, a complex set of in vitro tests, including production of reactive oxygen species, comet assay, cell cycle determination, gene expression, and cellular uptake, were utilized. It was found that the cytotoxic effect of MagAlg-DOX system is delayed compared to free DOX in both cell lines. This was attributed to the different mechanism of internalization of DOX and MagAlg-DOX into the cells, together with the fact that the drug is strongly bound on the drug nanocarriers. We discovered that nanoparticles can attenuate or even inhibit the effect of DOX, particularly in the tumor MCF7 cell line. This is a first comprehensive study on the cytotoxic effect of DOX-loaded SPIO compared with free DOX on healthy and cancer cell lines, as well as on the induced changes in gene expression.

Mesenchymal stromal cell labeling by new uncoated superparamagnetic maghemite nanoparticles in comparison with commercial Resovist--an initial in vitro study

OBJECTIVE

Cell therapies have emerged as a promising approach in medicine. The basis of each therapy is the injection of 1-100×10(6) cells with regenerative potential into some part of the body. Mesenchymal stromal cells (MSCs) are the most used cell type in the cell therapy nowadays, but no gold standard for the labeling of the MSCs for magnetic resonance imaging (MRI) is available yet. This work evaluates our newly synthesized uncoated superparamagnetic maghemite nanoparticles (surface-active maghemite nanoparticles - SAMNs) as an MRI contrast intracellular probe usable in a clinical 1.5 T MRI system.

METHODS

MSCs from rat and human donors were isolated, and then incubated at different concentrations (10-200 μg/mL) of SAMN maghemite nanoparticles for 48 hours. Viability, proliferation, and nanoparticle uptake efficiency were tested (using fluorescence microscopy, xCELLigence analysis, atomic absorption spectroscopy, and advanced microscopy techniques). Migration capacity, cluster of differentiation markers, effect of nanoparticles on long-term viability, contrast properties in MRI, and cocultivation of labeled cells with myocytes were also studied.

RESULTS

SAMNs do not affect MSC viability if the concentration does not exceed 100 μg ferumoxide/mL, and this concentration does not alter their cell phenotype and long-term proliferation profile. After 48 hours of incubation, MSCs labeled with SAMNs show more than double the amount of iron per cell compared to Resovist-labeled cells, which correlates well with the better contrast properties of the SAMN cell sample in T2-weighted MRI. SAMN-labeled MSCs display strong adherence and excellent elasticity in a beating myocyte culture for a minimum of 7 days.

CONCLUSION

Detailed in vitro tests and phantom tests on ex vivo tissue show that the new SAMNs are efficient MRI contrast agent probes with exclusive intracellular uptake and high biological safety.

Activation of HLA-G expression by 5-aza-2 - deoxycytidine in malignant hematopoetic cells isolated from leukemia patients

Human leukocyte antigen - G (HLA-G) is a non-classical HLA class I antigen with restricted distribution in normal tissues. Ectopic HLA-G expression observed at some pathological circumstances as malignant transformation might be triggered by epigenetic modifications such as DNA demethylation. Recently it was demonstrated that DNA methyltransferase inhibitor 5-aza-2 - deoxycytidine (AdC) induces/enhances HLA-G transcription in many leukemia cell lines of different origin. Here we investigated the effect of AdC on HLA-G expression in malignant hematopoetic cells isolated from patients with acute myeloid leukemia (AML) and chronic lymphocytic leukemia (B-CLL). We detected HLA-G expression in untreated cells from some patients. Nevertheless treatment with 5-aza-2 - deoxycytidine enhanced HLA-G transcription and concomitantly HLA-G protein synthesis in some leukemia cells.

Modulation of HLA-G expression

Recent studies demonstrated that HLA-G transcription is in some cells silenced by epigenetic mechanisms as DNA methylation and histone modification. Accordingly HLA-G gene transcriptions can be activated in such cells by demethylating agent or by inhibitors of histone deacetylation. In addition to epigenetic alterations HLA-G gene transcription can be activated by stress. In the present study these aspects of HLA-G expression are re-examined and a new inhibitor of histone deacetylation (valproic acid) and hypoxia mimetic chemical (CoCl2) are included. The highest activation of HLA-G transcription was achieved by treatment of choriocarcinoma JAR and lymphoblastoid RAJI cell lines with demethylating agent 5-aza-2 - deoxycytidine. Treatment of JAR and RAJI cells with histone deacetylase inhibitors (sodium butyrate and valproic acid) also enhanced HLA-G transcription. Nevertheless this increase in HLA-G expression was low as compared with activation by 5-aza-2 - deoxycytidine. The hypoxia mimetic agents (desferrioxamine or CoCl2) had no detectable effect on HLA-G gene transcription in examined cells. Relatively high increase of HLA-G transcription was detected in JAR and RAJI cells exposed to heat shock treatment. Interestingly heat shock induced high expression of HLA-G6 transcript in JAR cells. Heat shock treatment had no effect on alternative splicing of constitutively expressed HLA-G mRNA in choriocarcinoma cell line JEG-3. HLA-G1 protein expression was induced in JAR and RAJI cell lines by 5-aza-2 - deoxycytidine. In agreement with the differences in the levels of HLA-G transcripts JAR cells express more of HLA-G1 protein than RAJI cells.

Antibodies directed against the MHC-I molecule H-2Dd complexed with an antigenic peptide: similarities to a T cell receptor with the same specificity

alphabeta TCRs, which use an Ab-like structure to form a combining site, recognize molecular complexes consisting of peptides bound to MHC class I (MHC-I) or class II (MHC-II) molecules. To explore the similarities and differences between Ab and T cell recognition of similar structures, we have isolated two mAbs, KP14 and KP15, that specifically bind H-2D(d) complexed with an HIV envelope gp160-derived peptide, P18-I10. These Abs are MHC and peptide specific. Fine specificity of mAb binding was analyzed using a panel of synthetic peptides, revealing similarities between the mAb and a cloned TCR with the same specificity. These two mAbs used the same V(H) and J(H) gene segments, but different D, Vkappa, and Jkappa genes. Administered in vivo, mAb KP15 blocked the induction of CTL specific for recombinant vaccinia virus-encoded gp160, indicating its ability to bind endogenously generated MHC/peptide complexes. Analysis of the fine specificity of these mAbs in the context of their encoded amino acid sequences and the known three-dimensional structure of the H-2D(d)/P18-I10 complex suggests that they bind in an orientation similar to that of the TCR. Thus, the plasticity of the B cell receptor repertoire and the structural similarities among BCR and TCR allow Abs to effectively mimic alphabeta TCRs. Such mAbs may be useful in the therapeutic modulation of immune responses against infectious agents or harmful self Ags as well as in tracing steps in Ag processing.

Rigidification of the alpha2 helix of an MHC class I molecule by a valine to proline mutation in position 165 does not prevent peptide-specific antigen presentation

Although classical MHC class I glycoproteins bind peptide Ags for display at the cell surface, some MHC class I-related molecules such as the neonatal Fc receptor (FcRn) execute their function without binding peptide ligands. The three-dimensional structure of the FcRn suggested that a substitution of the conserved valine at position 165 of the alpha2 helix by proline contributed to a kink in the position of this helix relative to the alpha1 helix, and resulted in closing of the potential peptide-binding cleft. To test the contribution of proline 165 to the occlusion of the cleft and the binding of potential antigenic peptides, we introduced this mutation into the classical murine MHC class I molecule, H-2Dd, and characterized the ability of such a mutant to present peptide Ags to either a peptide-specific, H-2Dd-restricted T cell hybridoma (B4.2.3), or an allospecific, peptide-dependent, T cell hybridoma (3DT52.5.8). We show that the V165P mutation, expressed at the cell surface either in H-2Dd or in a single chain membrane version of H-2Dd, fails to eliminate recognition of the peptide/MHC complexes by two different T cells. Evaluation of a panel of synthetic substituted peptides suggests that subtle differences in the fine specificity of presentation can be discerned. Thus, the proline substitution at position 165 of FcRn and some other class I-like molecules is not the sole cause of the lack of peptide presentation.

Rigidification of the alpha2 helix of an MHC class I molecule by a valine to proline mutation in position 165 does not prevent peptide-specific antigen presentation

Although classical MHC class I glycoproteins bind peptide Ags for display at the cell surface, some MHC class I-related molecules such as the neonatal Fc receptor (FcRn) execute their function without binding peptide ligands. The three-dimensional structure of the FcRn suggested that a substitution of the conserved valine at position 165 of the alpha2 helix by proline contributed to a kink in the position of this helix relative to the alpha1 helix, and resulted in closing of the potential peptide-binding cleft. To test the contribution of proline 165 to the occlusion of the cleft and the binding of potential antigenic peptides, we introduced this mutation into the classical murine MHC class I molecule, H-2Dd, and characterized the ability of such a mutant to present peptide Ags to either a peptide-specific, H-2Dd-restricted T cell hybridoma (B4.2.3), or an allospecific, peptide-dependent, T cell hybridoma (3DT52.5.8). We show that the V165P mutation, expressed at the cell surface either in H-2Dd or in a single chain membrane version of H-2Dd, fails to eliminate recognition of the peptide/MHC complexes by two different T cells. Evaluation of a panel of synthetic substituted peptides suggests that subtle differences in the fine specificity of presentation can be discerned. Thus, the proline substitution at position 165 of FcRn and some other class I-like molecules is not the sole cause of the lack of peptide presentation.

A three-domain T cell receptor is biologically active and specifically stains cell surface MHC/peptide complexes

We have expressed in bacteria a single-chain T cell receptor (scTCR) with specificity for an HIV gp120-derived peptide bound to the murine MHC-I molecule, H-2Dd. This scTCR consists of V alpha covalently linked to the VbetaCbeta domains that was solubilized, refolded, and purified in high yield. Specific binding of the scTCR to MHC/peptide complexes was demonstrated by surface plasmon resonance, with a Kd of 2 to 8 x 10(-6) M. This scTCR specifically inhibited T cell activation, and stained cell surface MHC/peptide complexes as measured by cytofluorimetry. The preservation of binding specificity by such a three-domain scTCR suggests that this structure is sufficient for specific MHC/peptide recognition and that this strategy will be of general use as applied to other TCR.

A three-domain T cell receptor is biologically active and specifically stains cell surface MHC/peptide complexes

We have expressed in bacteria a single-chain T cell receptor (scTCR) with specificity for an HIV gp120-derived peptide bound to the murine MHC-I molecule, H-2Dd. This scTCR consists of V alpha covalently linked to the VbetaCbeta domains that was solubilized, refolded, and purified in high yield. Specific binding of the scTCR to MHC/peptide complexes was demonstrated by surface plasmon resonance, with a Kd of 2 to 8 x 10(-6) M. This scTCR specifically inhibited T cell activation, and stained cell surface MHC/peptide complexes as measured by cytofluorimetry. The preservation of binding specificity by such a three-domain scTCR suggests that this structure is sufficient for specific MHC/peptide recognition and that this strategy will be of general use as applied to other TCR.

Dissociation of beta 2-microglobulin is responsible for selective reduction of HLA class I antigenicity following acid treatment of cells

Beta 2-Microglobulin (beta 2 m) dissociated from surface HLA class I complex following exposure of cells to low pH and was detected in supernatant by radioimmunoprecipitation with specific monoclonal antibodies (mAbs). As the concn of beta 2m in supernatant increased, the binding of mAbs, specific for HLA class I heavy chains associated with beta 2m, to the cell surface declined. Binding of mAb specific for free HLA class I heavy chain to the cell surface increased after acid treatment. Reassociation with exogenous beta 2m confirmed increase in the number of free HLA class I heavy chains on surface of the cells after their exposure to low pH and also at least partially restored the reactivity with mAbs specific to HLA class I heavy chains associated with beta 2m. Dissociation of beta 2m from CD1 complex following acid treatment was also accompanied with the changes in antigenicity of cell surface CD1 molecules.

Use of Brefeldin A to localize block in intracellular transport of vesicular stomatitis virus G protein on interferon-treated cells

Brefeldin A (BFA) induced a rapid redistribution of vesicular stomatitis virus G protein (VSV-G) to the endoplasmatic reticulum (ER) in interferon (IFN)-pretreated cells. This result is consistent with accumulation of VSV-G in the trans-Golgi (GC) complex in cells pretreated with IFN and implies that IFN does not interfere with the ability of BFA to induce redistribution of proteins from GC to ER.

Integrin expression in human melanoma cell lines: heterogeneity of vitronectin receptor composition and function

Ten human melanoma cell lines were examined for integrin-receptor expression using a panel of antibodies directed against different integrin subunits. Considerable heterogeneity was detected for levels of expression of 7 integrins, including the alpha v beta 3 vitronectin receptor where a correlation between tumorigenic capacity in athymic nude mice and alpha v beta 3 levels was found. Detailed analysis of the vitronectin receptor on these lines revealed heterogeneity of composition. In one cell line, VUP, an alpha v beta 1 association was detected and, by antibody-inhibition studies, this receptor was shown to bind vitronectin as its ligand. In another line, DX3, evidence was obtained which indicated that apart from the alpha v beta 3 receptor the alpha v was able to associate with another beta subunit which was not beta 3. The existence of these alternative forms of the vitronectin receptor in this small sample of tumours of common origin might explain why the capacity to bind to fibrinogen and vitronectin substrates by these cells did not necessarily correlate with alpha v beta 3 levels.

Expression of HLA-DR mRNA in T cells following activation is early and can precede DNA synthesis

The stimulation of T cells is accompanied by the appearance of a number of activation antigens not found on resting T cells. We have studied the expression of one group of such antigens, the HLA class II antigens (DR, DQ and DP), following stimulation with PHA and PMA. Immunofluorescence studies using monoclonal antibodies indicated that cell surface class II determinants were detectable as little as 30 minutes following stimulation, and that their levels remained constant for about 24 hours, after which they began to increase. Studies on the molecule level demonstrated an increase in the steady state levels of mRNA for DR beta by 15 minutes. Immunoblot analysis of resting T cell lysates using a monoclonal antibody reactive with DR detected a polypeptide of approximately 28 KDa, which agrees with the known molecular mass of the light chain of class II molecules on SDS-PAGE, suggesting that the rapid surface expression might have been due to the presence of pre-formed class II polypeptides. These results demonstrate 1) that T cells defined as resting by conventional criteria contain class II polypeptides and 2) that increases in steady state levels of class II mRNA is a very early event which precedes the initiation of DNA synthesis.