Peptide-specific T cell clonal expansion in vivo following immunization in the eye, an immune-privileged site

To visualize the primary antigen-specific T cell response to Ag introduced into the eye, we have used an adoptive transfer system in which a limiting number of OVA peptide (323-339)-specific T cells from a TCR-transgenic mouse were transferred into nonirradiated, syngeneic recipients and then tracked in vivo by staining for FACS analysis or immunohistochemistry with the clonotypic mAb KJ1-26. Following posterior chamber injection of Ag, KJ1-26+ cells accumulated primarily in the draining, submandibular lymph node (LN) within 3 days. Although reduced in number, by day 6 these cells were primarily in the paracortical regions and were able to proliferate and secrete IL-2 in response to Ag stimulation. In contrast, following i.v. injection of Ag, the KJ1-26+ cells accumulated in the paracortical regions of the LN to a comparable degree, but did not proliferate or secrete IL-2. The day 3 accumulation of KJ1-26+ cells in the submandibular LN was inhibited if the eye was removed within 5 h after injection of Ag. In the spleen, foci of KJ1-26+ cells were observed in the periarteriolar lymphoid sheaths at day 3; these were not observed to the same degree following other forms of immunization. These results demonstrate that the submandibular LN is the primary site for early clonal expansion of antigen-specific T cells following intraocular Ag administration and that these cells show changes consistent with immunity rather than tolerance.

Transgenic expression of IFN-gamma in the murine lens results in multiple ocular abnormalities and an early but self-limited inflammatory response

The anterior chamber of the eye is known to be an immune privileged site, due to both local and systemic effects on the immune response. Injection of IFN-gamma into the anterior chamber (AC) overcomes the suppression of antigen-specific delayed hypersensitivity responses normally seen in the eye. Transgenic mice expressing increased IFN-gamma in the lens under the alpha A-crystallin promoter were produced to determine whether the proinflammatory effects of IFN-gamma would abolish immune privilege and promote loss of tolerance as has been seen in non-immune privileged tissues. Two alpha C/IFN-gamma transgenic lines are described which demonstrate multiple ocular and lenticular abnormalities some of which are developmental in origin and others that may be secondary to the inflammatory effects of IFN-gamma. A significant inflammatory cell infiltrate which is observed in the AC and vitreous from birth to 4 weeks of age, consists initially of macrophage and polymorphonuclear leukocytes and then CD4+ T lymphocytes. However, the infiltrate is essentially resolved by 6 weeks of age. Therefore, although lens-specific expression of IFN-gamma results in early loss of immune privilege, chronic uveitis does not occur probably due to the lack of continued IFN-gamma expression.

Characterization of human T-cell responses to Yersinia enterocolitica superantigen

We reported that antigenic preparations from Yersinia enterocolitica stimulate murine T cells in a manner consistent with that of superantigens. As a consequence we examined whether Y. enterocolitica antigenic preparations stimulate human T-cell cultures. Human T cells, enriched from peripheral blood lymphocytes, were stimulated to proliferate in the presence of Y. enterocolitica cytoplasmic and membrane preparations. This activity has also been shown to be sensitive to protease treatment, indicating the presence of a protein, and when separated by ion-exchange chromatography a single peak of activity is resolved. Furthermore, this proliferation was inhibited, in a dose-dependent manner, by the presence of antibodies directed against MHC class II antigens, indicating a requirement for these molecules. When these cells were stained with a panel of V beta-specific antibodies to determine if there was an enrichment of a particular V beta-bearing T-cell subset after stimulation, results indicate a significant enrichment of T cells bearing V beta 3, V beta 12, V beta 14, and V beta 17 over controls. Taken together, these data are consistent with a Y. enterocolitica product acting as a superantigen for human T cells.

Lens-specific expression of a major histocompatibility complex class I molecule disrupts normal lens development and induces cataracts in transgenic mice

PURPOSE

Lens epithelial tissue does not normally express major histocompatibility complex (MHC) class I molecules. In addition, the mechanism of self-tolerance to intraocular antigens is unknown. To study the effect of class I expression in the lens, transgenic mice were produced that express an allo-MHC class I molecule under the alpha A-crystallin proximal promoter.

METHODS

p alpha Dd was generated by fusion of the H-2Dd structural gene to the alpha A-crystallin proximal promoter. Transgenic mice were produced, and founder lines were identified by Southern blot hybridization. Eyes from transgenic mice were cryostat sectioned and stained for Dd expression or fixed in paraformaldehyde and stained for histologic analysis. Lens RNA was isolated by acid phenol extraction, and transgene expression was analyzed by nuclease protection.

RESULTS

The transgenic mice demonstrated dose-dependent, nonimmunologic lens defects consistent within a given line. In the highest expressing lines, ocular defects, including microphthalmia and cataract formation, were observed. Many adult mice from these lines demonstrated lens capsule rupture and a Dd-specific inflammatory response. Inflammation did not occur in mice with intact lens capsules.

CONCLUSIONS

Overexpression of H-2Dd in the lens had serious nonimmunologic consequences on lens development and cataract formation. In addition, the high copy number mice revealed at least a partial loss of immunologic tolerance on lens capsule rupture. The lack of an inflammatory response in transgenic mice with intact lens capsules suggests that the physical barrier of the lens capsule is one mechanism of maintaining immune privilege.

Transcription of the murine class II Eb gene is regulated primarily at the level of transcriptional initiation

The constitutive and inducible expression of MHC class II genes is known to be regulated by multiple upstream promoter elements. Transient transfection assays implicate the proximal promoter region as both necessary and sufficient for appropriate tissue-specific and inducible expression. However, transgenic mouse experiments suggest that additional control regions are important. In this study we tested the hypothesis that additional regulation of class II expression occurred at the level of RNA polymerase II elongation. Nuclear run-on analysis using single-stranded probes spanning the entire Eb gene was performed on a variety of class II-positive, class II-negative, and class II-inducible cell lines. The results demonstrate that, while there is not an even distribution of RNA polymerase along the gene, there is no evidence for a regulated block in elongation. These data further support the idea that the primary mechanism of class II gene regulation is at the level of transcriptional initiation.

Characterization of MHC induction by Mycoplasma fermentans (incognitus strain)

Mycoplasma fermentans (incognitus strain) is a recently identified new human pathogen and suspected cofactor in acquired immune deficiency syndrome. Because this organism appears to exert strong immunosuppressive properties of its own, we decided to investigate whether it was capable of inducing MHC class II expression, as we have observed for other species of mycoplasma. In this report we demonstrate that M. fermentans (incognitus strain) is capable of producing factors that increase MHC class II expression as well as MHC class I expression on the myelomonocytic cell line, WEHI-3 cells. We also present data showing that these mycoplasmal factors induce small, although significant, increases in MHC class I and II antigens on a mouse glioma cell line, G26-20, and MHC class II expression on the human monocyte cell lines, U-937 and HL-60. Using nuclear run-on analysis, we show that the mycoplasma-induced increase in MHC expression is at least partially due to an increase in transcription of the MHC genes. Furthermore, we show that the factor that mediates this activity is sensitive to protease treatment, indicating that it is, at least in part, protein. These results demonstrate that M. fermentans (incognitus strain) is capable of modulating the expression of immunologically important MHC genes in both murine and human cell lines, which may prove to be an important factor in the pathogenesis of this organism.

Two regions of the H-2 Dd promoter are responsive to dimethylsulfoxide in line 1 cells by a mechanism distinct from IFN-gamma

The line 1 lung carcinoma is a spontaneous BALB/c tumor deficient in class I Ag expression at the protein and mRNA levels. Exposure of line 1 cells to 3% DMSO or IFN-gamma increases class I Ag protein and mRNA dramatically. We have examined the regulation of class I Ag induction by DMSO in line 1 cells. We found DMSO induces class I Ag expression in line 1 cells by a mechanism distinct from IFN, because the kinetics of class I Ag induction by these agents were dramatically different, 7 days vs 3 days, and DMSO did not act through an IFN second messenger. At the molecular level, class I H chain transcription in line 1 cells was low. Treatment with 3% DMSO or IFN-gamma increased H chain transcription four-fold and sevenfold, respectively, indicating that class I H chain expression is regulated at the level of transcription in line 1 cells. Using reporter gene constructs, we mapped the regions in the Dd H chain promoter that increase H chain expression after DMSO treatment of line 1 cells. Two regions of the Dd promoter, D1, from -210 to -133 bp, and D2, from -125 to -61 bp, were found to be independently responsive to DMSO. These regions were also responsive to IFN-gamma in line 1 cells. However, consistent with our cellular results, DMSO and IFN induction of class I H chain expression differed at the molecular level as determined by D1 point mutations that diminished IFN-gamma responsiveness but did not alter induction by DMSO. Thus, DMSO appears to regulate class I transcription through multiple regions of the class I H chain promoter in line 1 cells by a mechanism distinct from IFN-gamma.

Two regions of the H-2 Dd promoter are responsive to dimethylsulfoxide in line 1 cells by a mechanism distinct from IFN-gamma

The line 1 lung carcinoma is a spontaneous BALB/c tumor deficient in class I Ag expression at the protein and mRNA levels. Exposure of line 1 cells to 3% DMSO or IFN-gamma increases class I Ag protein and mRNA dramatically. We have examined the regulation of class I Ag induction by DMSO in line 1 cells. We found DMSO induces class I Ag expression in line 1 cells by a mechanism distinct from IFN, because the kinetics of class I Ag induction by these agents were dramatically different, 7 days vs 3 days, and DMSO did not act through an IFN second messenger. At the molecular level, class I H chain transcription in line 1 cells was low. Treatment with 3% DMSO or IFN-gamma increased H chain transcription four-fold and sevenfold, respectively, indicating that class I H chain expression is regulated at the level of transcription in line 1 cells. Using reporter gene constructs, we mapped the regions in the Dd H chain promoter that increase H chain expression after DMSO treatment of line 1 cells. Two regions of the Dd promoter, D1, from -210 to -133 bp, and D2, from -125 to -61 bp, were found to be independently responsive to DMSO. These regions were also responsive to IFN-gamma in line 1 cells. However, consistent with our cellular results, DMSO and IFN induction of class I H chain expression differed at the molecular level as determined by D1 point mutations that diminished IFN-gamma responsiveness but did not alter induction by DMSO. Thus, DMSO appears to regulate class I transcription through multiple regions of the class I H chain promoter in line 1 cells by a mechanism distinct from IFN-gamma.

Yersinia enterocolitica produces superantigenic activity

We have recently observed that antigenic preparations from Yersinia enterocolitica are capable of inducing strong proliferative responses in normal murine spleen cell cultures. As a consequence of this observation, we evaluated whether Yersinia-derived Ag possess superantigenic activity. Stimulatory activity can be found in culture supernatants, as well as membrane and cytoplasmic fractions of Y. enterocolitica. Cell depletion studies indicate that the primary responding cell is a CD4+ T cell, which requires the presence of APC for responsiveness to Y. enterocolitica Ag. Furthermore, these APC must express MHC class II Ag, as evidenced by the fact that either antibody depletion of class II+ APC or addition of anti-class II antibodies (that block class II Ag on the surface of APC) eliminates the proliferative response. Evaluation of TCR usage by BALB/c T cells responsive to Y. enterocolitica revealed that those T cells bearing V beta 3, 6, and 11 and possibly 7 and 9 were expanded after exposure to Y. enterocolitica Ag preparations. By using a panel of T cell hybridomas, we have shown that hybridomas bearing V beta 3, 7, 8.1, 9, and 11 but not 2, 8.2, 8.3, and 13 respond to Yersinia. When cytoplasmic fractions of Y. enterocolitica were subjected to column chromatography, proliferative activity was enriched approximately 27-fold, and the elution characteristics of the active material suggest that it possesses hydrophobic regions and is, therefore, probably membrane associated. These data indicate that Y. enterocolitica produces antigenic material that has properties consistent with those of T cell superantigens.

Yersinia enterocolitica produces superantigenic activity

We have recently observed that antigenic preparations from Yersinia enterocolitica are capable of inducing strong proliferative responses in normal murine spleen cell cultures. As a consequence of this observation, we evaluated whether Yersinia-derived Ag possess superantigenic activity. Stimulatory activity can be found in culture supernatants, as well as membrane and cytoplasmic fractions of Y. enterocolitica. Cell depletion studies indicate that the primary responding cell is a CD4+ T cell, which requires the presence of APC for responsiveness to Y. enterocolitica Ag. Furthermore, these APC must express MHC class II Ag, as evidenced by the fact that either antibody depletion of class II+ APC or addition of anti-class II antibodies (that block class II Ag on the surface of APC) eliminates the proliferative response. Evaluation of TCR usage by BALB/c T cells responsive to Y. enterocolitica revealed that those T cells bearing V beta 3, 6, and 11 and possibly 7 and 9 were expanded after exposure to Y. enterocolitica Ag preparations. By using a panel of T cell hybridomas, we have shown that hybridomas bearing V beta 3, 7, 8.1, 9, and 11 but not 2, 8.2, 8.3, and 13 respond to Yersinia. When cytoplasmic fractions of Y. enterocolitica were subjected to column chromatography, proliferative activity was enriched approximately 27-fold, and the elution characteristics of the active material suggest that it possesses hydrophobic regions and is, therefore, probably membrane associated. These data indicate that Y. enterocolitica produces antigenic material that has properties consistent with those of T cell superantigens.

Differential induction of bone marrow macrophage proliferation by mycoplasmas involves granulocyte-macrophage colony-stimulating factor

We have studied the ability of three different Mycoplasma species to induce proliferation of bone marrow-derived macrophages (BMM). We observed a significant mitogenic effect when BMM cells from BALB/c, DBA/2J, SJL, and C57BL/6 mice were incubated with membranes derived from Mycoplasma arginini or M. arthritidis but not when they were incubated with an equivalent amount of M. pulmonis membrane. We also determined that pretreatment of mycoplasma membrane preparations with papain eliminated the ability of these preparations to induce BMM proliferation. To determine whether these membrane fractions acted indirectly by stimulating the production of soluble factors known to stimulate proliferation of BMM cells, we performed blocking studies with antibodies directed against colony-stimulating factor 1 (CSF-1), interleukin-3 (IL-3), and granulocyte-macrophage colony-stimulating factor. Our results indicate that antibodies directed against either CSF-1 or IL-3 failed to block mycoplasma-initiated proliferation of BMM cells. However, when anti-GM-CSF was added to proliferative cultures at the time of initiation, we saw a dose-dependent reduction of mycoplasma-initiated proliferation. We conclude that the ability of mycoplasma membranes to initiate the proliferation of BMM is not shared by all species of mycoplasma and that it involves the production of GM-CSF by an as yet undetermined cell.

Evidence that IFN-gamma does not affect MHC class II gene expression at the post-transcriptional level in a mouse macrophage cell line

Mouse class II major histocompatibility complex genes have been shown to be regulated at the level of transcription for both tissue-specific and inducible expression. In particular, IFN-gamma induction of the class II genes has been shown to occur at the transcriptional level, although the role that additional post-transcriptional mechanisms of regulation may play in this induction is not known. To evaluate IFN-gamma effects on transcriptional and post-transcriptional events of class II gene expression, we examined the rate of decline of class II transcription, steady-state mRNA, and cell surface protein following the removal of IFN-gamma from maximally stimulated WEHI-3 cells (an IFN-gamma inducible, myelomonocytic cell line). We determined that transcription of class II genes almost completely returned to baseline levels eight hours after removal of IFN-gamma. However, the steady-state level of class II mRNA's required 4 days, and membrane Ia expression required 5 days to return to baseline levels. This decay was linear and allowed us to determine a half-life value of 16-20 h for class II transcripts. These data demonstrate that, following removal of IFN-gamma from fully stimulated cells, transcription of the class II genes declined rapidly, but mRNA was quite long-lived. We also assessed the class II mRNA stability in unstimulated WEHI-3 cells and the B-cell lymphoma. A20/2J, by actinomycin D treatment and northern blot analysis. In agreement with the IFN-gamma washout experiments, transcripts from all four class II genes were quite long-lived in these cell types, with a half-life greater than ten hours. These data support the concept that IFN-gamma acts primarily at the level of class II transcription and argues against IFN-gamma playing a major role in post-transcriptional modulation of class II expression.

Negative trans-acting factors extinguish Ia expression in B cell-L 929 somatic cell hybrids

Numerous studies have implicated trans-acting factors in the regulation of MHC class II gene expression. Some of these factors have been shown to act by inducing the expression of class II genes while others have been demonstrated to downregulate such expression. These reports have dealt almost exclusively with the role of trans-acting factors in the regulation of class II gene expression in hematopoietic-derived cells. We decided to extend these studies to the role trans-acting factors play in nonhematopoietic-derived (NHD) cells. In order to address this question we made somatic cell hybrids between the NHD Ltk- cell line and normal B cells to determine if the existence of positive trans-acting factors from the B cell would lead to the expression of Ltk- class II genes in the resultant hybrid. Our results clearly indicate that not only was there no induction of Ltk- class II gene expression in the hybrids, but there was a loss of B cell class II gene expression as well. These results suggest that Ltk- cells possess negative trans-acting factors that appear to predominate over the positive trans-acting factors possessed by B cells. We have further extended these studies to test the MHC-inducing activity of IFN-gamma and IL-4 on these hybrids. Our results indicate that the hybrids responded to IFN-gamma with an increase in class I but not class II expression for both fusion partners. Furthermore, neither B cell nor L cell class II genes were induced by IL-4. Taken together, these results indicate that Ltk- cells possess negative trans-acting factors that not only maintain the Ia- phenotype of these cells, but also block the action of positive trans-acting factors from B cells.

MHC class II transcription in different mouse cell types. Differential requirement for protein synthesis between B cells and macrophages

Although the MHC class II genes are known to be regulated transcriptionally, the relative rates of transcription of the four classical class II genes in different cell types have not been investigated. Using nuclear transcriptional analysis, we have investigated the transcriptional rates of the class II genes in the macrophage cell line WEHI-3, normal bone marrow-derived macrophages, L-929 cells, and two different B cell lymphoma lines. Kinetic analysis of class II transcription in IFN-gamma-treated WEHI-3 cells revealed a 4-h delay, followed by a rapid increase in transcription over the next 20 h. A significant basal level of class II transcription, apparent in bone marrow derived macrophages, was also further enhanced by IFN-gamma treatment. None of the class II genes were transcribed in L cells, whereas all class II genes were transcribed constitutively in the B cell lines. In both B cell lines and macrophages, the four class II genes were found to be transcribed at different rates from one another, but the only gene showing a consistent pattern in multiple experiments was A-alpha, always showing the highest rate. We also investigated the effect of protein synthesis inhibition on class II transcription. Cycloheximide treatment of WEHI-3 cells did not inhibit IFN-gamma-induced transcription of the class II genes within 8 h, suggesting that IFN-gamma acts on pre-existing trans-acting factors, rather than inducing their synthesis. In contrast, treatment of B cells with cycloheximide for 8 h significantly reduced class II transcription, suggesting that, in B cells, continuous synthesis of a labile trans-acting factor is required for constitutive expression. These data support the notion that class II expression in B cells is mediated by trans-acting factors distinct from those found in macrophages.

MHC class II transcription in different mouse cell types. Differential requirement for protein synthesis between B cells and macrophages

Although the MHC class II genes are known to be regulated transcriptionally, the relative rates of transcription of the four classical class II genes in different cell types have not been investigated. Using nuclear transcriptional analysis, we have investigated the transcriptional rates of the class II genes in the macrophage cell line WEHI-3, normal bone marrow-derived macrophages, L-929 cells, and two different B cell lymphoma lines. Kinetic analysis of class II transcription in IFN-gamma-treated WEHI-3 cells revealed a 4-h delay, followed by a rapid increase in transcription over the next 20 h. A significant basal level of class II transcription, apparent in bone marrow derived macrophages, was also further enhanced by IFN-gamma treatment. None of the class II genes were transcribed in L cells, whereas all class II genes were transcribed constitutively in the B cell lines. In both B cell lines and macrophages, the four class II genes were found to be transcribed at different rates from one another, but the only gene showing a consistent pattern in multiple experiments was A-alpha, always showing the highest rate. We also investigated the effect of protein synthesis inhibition on class II transcription. Cycloheximide treatment of WEHI-3 cells did not inhibit IFN-gamma-induced transcription of the class II genes within 8 h, suggesting that IFN-gamma acts on pre-existing trans-acting factors, rather than inducing their synthesis. In contrast, treatment of B cells with cycloheximide for 8 h significantly reduced class II transcription, suggesting that, in B cells, continuous synthesis of a labile trans-acting factor is required for constitutive expression. These data support the notion that class II expression in B cells is mediated by trans-acting factors distinct from those found in macrophages.

Induction of class II MHC antigen expression in macrophages by Mycoplasma species

Several different Mycoplasma species have been shown to act as mitogens for either T or B cells and as stimulators of macrophage tumoricidal activity. In this report, we show that at least five different species of Mycoplasma are capable of inducing class II MHC expression on macrophages. We have observed significant induction of class II MHC surface expression on the myelomonocytic cell line, WEHI-3, as early as 24 h after deliberate infection of cultures, reaching maximal levels by 4 days. This induction was also apparent at the mRNA level as assessed by Northern blot analysis by using A alpha, E alpha, and A beta probes. However, unlike many other previously described MHC-inducing agents, mycoplasmas failed to induce class I MHC expression at either the cell surface or mRNA levels. Kinetic analysis revealed that induction of class II mRNA by mycoplasmas was slower than induction by IFN-gamma requiring 24 h rather than 8 h for significant increases to be noted. Induction by mycoplasmas does not require the presence of live organisms and remains active after heat treatment of 90 degrees C for 30 min. We have also demonstrated that mycoplasma infection of primary bone marrow macrophage cultures leads to the induction of both class I and class II genes and, as in the case of WEHI-3, this induction does not require the presence of live organisms. These data indicate that several Mycoplasma species have the capacity to induce class II MHC expression in WEHI-3 and both class I and class II MHC expression in bone marrow macrophage cultures in the absence of any T cell products.

Induction of class II MHC antigen expression in macrophages by Mycoplasma species

Several different Mycoplasma species have been shown to act as mitogens for either T or B cells and as stimulators of macrophage tumoricidal activity. In this report, we show that at least five different species of Mycoplasma are capable of inducing class II MHC expression on macrophages. We have observed significant induction of class II MHC surface expression on the myelomonocytic cell line, WEHI-3, as early as 24 h after deliberate infection of cultures, reaching maximal levels by 4 days. This induction was also apparent at the mRNA level as assessed by Northern blot analysis by using A alpha, E alpha, and A beta probes. However, unlike many other previously described MHC-inducing agents, mycoplasmas failed to induce class I MHC expression at either the cell surface or mRNA levels. Kinetic analysis revealed that induction of class II mRNA by mycoplasmas was slower than induction by IFN-gamma requiring 24 h rather than 8 h for significant increases to be noted. Induction by mycoplasmas does not require the presence of live organisms and remains active after heat treatment of 90 degrees C for 30 min. We have also demonstrated that mycoplasma infection of primary bone marrow macrophage cultures leads to the induction of both class I and class II genes and, as in the case of WEHI-3, this induction does not require the presence of live organisms. These data indicate that several Mycoplasma species have the capacity to induce class II MHC expression in WEHI-3 and both class I and class II MHC expression in bone marrow macrophage cultures in the absence of any T cell products.

Induction of class I and class II MHC antigen expression on murine bone marrow-derived macrophages by IL-4 (B cell stimulatory factor 1)

We have studied the effects of IL-4 (B cell stimulatory factor 1) on the expression of MHC gene products in normal bone marrow-derived macrophages, peritoneal macrophages, and the myelomonocytic cell line WEHI-3. Using both IL-4-containing T cell supernatant and rIL-4, we have observed significant induction of both class I and class II MHC surface expression (about 1.5- to 4-fold increase) in 2-, 3-, and 4-day cultures of bone marrow-derived macrophages. This induction was also apparent at the mRNA level as assessed by Northern blot analysis using A beta, E alpha, and class I probes. Kinetic analysis revealed that induction of class II mRNA by IL-4 was slower than induction by IFN-gamma, requiring 48 h before a significant increase was noted. The magnitude of MHC induction by IL-4 was not as great as that seen with IFN-gamma, which was found to increase surface expression of MHC antigens two- to eightfold. IL-4 also differs from IFN-gamma in the repertoire of macrophages responsive to it. IL-4 was unable to induce class I or class II expression in either thioglycolate-elicited peritoneal macrophages or WEHI-3 cells whereas IFN-gamma induced MHC antigen expression on both cell types under the same conditions. These data demonstrate that IL-4 is capable of inducing both class I and class II MHC gene products in some, but not all, macrophages.

Induction of class I and class II MHC antigen expression on murine bone marrow-derived macrophages by IL-4 (B cell stimulatory factor 1)

We have studied the effects of IL-4 (B cell stimulatory factor 1) on the expression of MHC gene products in normal bone marrow-derived macrophages, peritoneal macrophages, and the myelomonocytic cell line WEHI-3. Using both IL-4-containing T cell supernatant and rIL-4, we have observed significant induction of both class I and class II MHC surface expression (about 1.5- to 4-fold increase) in 2-, 3-, and 4-day cultures of bone marrow-derived macrophages. This induction was also apparent at the mRNA level as assessed by Northern blot analysis using A beta, E alpha, and class I probes. Kinetic analysis revealed that induction of class II mRNA by IL-4 was slower than induction by IFN-gamma, requiring 48 h before a significant increase was noted. The magnitude of MHC induction by IL-4 was not as great as that seen with IFN-gamma, which was found to increase surface expression of MHC antigens two- to eightfold. IL-4 also differs from IFN-gamma in the repertoire of macrophages responsive to it. IL-4 was unable to induce class I or class II expression in either thioglycolate-elicited peritoneal macrophages or WEHI-3 cells whereas IFN-gamma induced MHC antigen expression on both cell types under the same conditions. These data demonstrate that IL-4 is capable of inducing both class I and class II MHC gene products in some, but not all, macrophages.

Analysis of the equine lymphocyte antigen system by Southern blot hybridization

Fourteen Standardbred horses homozygous for one of six equine lymphocyte antigen (ELA) specificities (A1, A3, A4, A5, A6, or A10) were analyzed by Southern blot hybridization using DNA probes derived from the mouse major histocompatibility complex (MHC). Total genomic DNA from peripheral lymphocytes was digested with the restriction enzymes Hind III, Pvu II, or Eco RI. Twenty-three to thirty-three bands were generated for individual horses with the class I cDNA probe. The resulting band patterns revealed 12-14 nonpolymorphic fragments, which is consistent with the highly conserved Qa/Tla genes seen in other species. The remaining 10-19 bands displayed significant polymorphism; no two animals had identical band patterns when studied with all three enzymes. The polymorphism was markedly decreased between animals of the same ELA serotypes. Unique bands were identified in both A1 horses and all four A6 animals. Pvu II digestions of lymphocyte DNA were hybridized with mouse MHC class II probes. A cDNA probe for the E alpha gene revealed only a single nonpolymorphic band. In contrast, a cDNA probe for the H-2 A alpha locus displayed three to five strong bands in each animal with polymorphism that was most pronounced between horses of different ELA serotypes. Genomic DNA probes for A beta and E beta genes both revealed multiple polymorphic bands. However, cross-hybridization between these two probes prevented distinction between A beta and E beta equivalent loci. The reduced polymorphism evident within ELA specificities is consistent with the concept that the equine lymphocyte antigen system includes two families of closely linked MHC genes.

Further characterization of low density mononuclear cells: FACS-assisted analysis of human MLR stimulators

Previously, we reported that all of the potent stimulators of the allogeneic mixed leukocyte reaction (MLR) are contained in a heterogeneous low density fraction of human peripheral blood mononuclear (PBM) cells. We have further characterized human MLR stimulators by staining them with highly specific monoclonal antibodies, and then analyzing and separating them with the fluorescence-activated cell sorter. These studies revealed two populations of low density cells with potent allogeneic stimulatory activity. One population is a monocyte subset that reacts with anti-OKM1, MO.2, and expresses C3b as well as Fc-IgG receptors. The second population exhibits even greater stimulatory capacity and does not express any of these monocyte markers. Moreover, these cells are not phagocytic and do not react with alpha-naphthyl esterase. They comprise approximately 10% of the low density fraction or 0.5% of PBM. These cells are most likely lymphoid dendritic cells, described in various species as potent MLR stimulators. In contrast to the allogeneic MLR, only the low density cell type exhibiting dendritic cell characteristics induced a potent autologous MLR.

Further characterization of low density mononuclear cells: FACS-assisted analysis of human MLR stimulators

Previously, we reported that all of the potent stimulators of the allogeneic mixed leukocyte reaction (MLR) are contained in a heterogeneous low density fraction of human peripheral blood mononuclear (PBM) cells. We have further characterized human MLR stimulators by staining them with highly specific monoclonal antibodies, and then analyzing and separating them with the fluorescence-activated cell sorter. These studies revealed two populations of low density cells with potent allogeneic stimulatory activity. One population is a monocyte subset that reacts with anti-OKM1, MO.2, and expresses C3b as well as Fc-IgG receptors. The second population exhibits even greater stimulatory capacity and does not express any of these monocyte markers. Moreover, these cells are not phagocytic and do not react with alpha-naphthyl esterase. They comprise approximately 10% of the low density fraction or 0.5% of PBM. These cells are most likely lymphoid dendritic cells, described in various species as potent MLR stimulators. In contrast to the allogeneic MLR, only the low density cell type exhibiting dendritic cell characteristics induced a potent autologous MLR.

Distinct epitopes are recognized by cytolytic T lymphocyte clones on the same class I molecule: direct demonstration using DNA-transfected targets and long-term cytolytic T cell clones

By producing long-term, stable, cytolytic T lymphocyte clones and utilizing targets expressing only a single gene product derived from the stimulator mouse strain, we have been able to directly demonstrate that T cells recognize distinct epitopes expressed on a single H-2 molecule. These multiple determinants are distinguishable by inhibition patterns with monoclonal antibodies (mAb). When two T cell clones, P-2.14 and P-2.17, are tested on an L cell transfected with the Dp gene (lambda 12a), the T cells kill the transfected targets as well as blasts derived from Dp mouse strains. mAb 7-16.10 inhibits recognition and killing of Dp targets by both P-2.14 and P-2.17. This mAb recognizes a private specificity H-2.m22. Interestingly mAb 11-20.3 which also recognizes the H-2.m22 specificity inhibits clone P-2.14 but not P-2.17. The mAb 7-16.10, however, competes with 11-20.3 for binding to the surface of L cells expressing the Dp gene. Thus the two T cells must recognize an overlapping specificity. Other mAb which bind to the H-2Dp molecule are unable to inhibit either of these two cytolytic T cell clones. Paradoxically, any of the mAb when tested individually are sufficient to inhibit the polyclonal response derived from in vitro mixed lymphocyte culture. Therefore, by using targets expressing only a single H-2 molecule derived by DNA-mediated gene transfer and cytolytic T cell clones we have been able to directly demonstrate the presence of multiple epitopes on a single molecule and define their inhibition with mAb directed to that same molecule.

Production and characterization of T cell clones specific for mouse hepatitis virus, strain JHM: in vivo and in vitro analysis

Mouse hepatitis virus, strain JHM, is a coronavirus capable of inducing both acute and chronic central nervous system disease. To characterize the cell-mediated immune response directed toward JHMV antigens, we have generated and analyzed the properties of four T cell clones reactive to JHMV antigens. All four clones are of the Ly-1+2- phenotype and show an antigen-specific, I-Ab-restricted proliferative response that is dependent on antigen-presenting cells (APC). The fine specificity of I-A restriction was revealed by their differential recognition of JHMV antigen in the context of mutant I-A molecules present on B6.C-H-2bm12 APC. Two clones were unable to recognize JHMV antigen presented on bm12 APC, whereas a third clone showed an equivalent response with both bm12 and wild type B6 APC. In the analysis of the viral specificity, three of the clones showed distinct cross-reactions with MHV-2 and very little if any cross-reaction with MHV-A59. In addition, three of three clones tested responded well to sucrose gradient-purified, UV-inactivated JHMV, indicating that their specificity is directed toward virus structural rather than nonstructural proteins. Finally, two of the clones were analyzed for their ability to induce a DTH reaction when injected together with antigen into the footpads of various mouse strains. Consistent with the in vitro data, both clones produced a marked DTH response only in those strains carrying the I-Ab genotype. These data demonstrate, both in vivo and in vitro, that at least one component of the cell-mediated immune response to JHMV is characterized by an Ly-1+2-, I-A-restricted T cell specific for JHMV structural proteins.