Rare peripheral T cells migrate to and persist in normal mouse thymus.

The traffic of T cells between the thymus and peripheral lymphoid organs is generally thought to be unidirectional. Using a technique of lymphocyte transfer between Thy-1 congenic mice, we demonstrate here the entry of rare peripheral lymph node T cells into the normal mouse thymus. At time points from 3 h to 24 wk after transfer, donor peripheral T cells were present in the host thymus, mainly as scattered single cells confined to the medulla. At 2 wk after transfer, donor T cells constituted 0.2% of the medullary thymocytes (compared with 11% of the peripheral lymph node T cells). As a population, these cells exhibited a stable mature immunophenotype (Ly-1hi, PNAlo, and mixed L3T4- and Lyt-2+). A minority of the donor T cells expressed high levels of the MEL-14 "homing receptor". The thymic medulla thus exhibits features of a peripheral lymphoid organ but differs in its low rate of turnover of recirculating T cells.

Intrathymic presentation of circulating non-MHC antigens by medullary dendritic cells. An antigen-dependent microenvironment for T cell differentiation.

We present evidence for intrathymic presentation of soluble circulating antigens in vivo. Our results show that proteins of different molecular weight enter the mouse thymus rapidly after i.v. injection. The intrathymic presence of antigen was assayed by proliferation of cloned antigen-specific T helper cells, which were cocultured with purified thymic stromal cells; stromal cells were isolated and purified as lymphostromal cell complexes, which preexist in vivo. Antigen presentation copurified with non-adherent medullary dendritic cells (DC) (interdigitating cells). I-A- cortical macrophages forming thymocyte rosettes in vivo and I-A+ cortical epithelial cells forming thymic nurse cells (TNC) in vivo did not act as antigen presenting cells (APC) after antigen pulsing in vivo or in vitro. Thymic APC turn over physiologically and are rapidly replaced (within 2-5 wk) after lethal irradiation by donor bone marrow-derived cells. The frequency of thymocyte-DC interactions in vivo strictly correlates with thymic T cell differentiation, and is independent of the immune status of the animal. Fetal thymic APC seem to be secluded from antigen in the maternal circulation. Thymic DC-ROS probably represent the microenvironment where maturing T cells first encounter non-MHC antigens in the context of self-MHC antigens.

T cell subsets defined by expression of Lyt-1,2,3 and Thy-1 antigens. Two-parameter immunofluorescence and cytotoxicity analysis with monoclonal antibodies modifies current views.

Using monoclonal antibodies and multiparameter fluorescence analyses, we show that the expression of Lyt-1, Lyt-2, and Lyt-3 on T cell subpopulations is more complex than was originally recognized by the cytotoxic depletion studies with conventional reagents that defined the Lyt-1+2+3+, Lyt-1+2-3-, and Lyt-1-2+3+ populations. We detect at least some Lyt-1 on all T (Thy-1-bearing) lymphocytes; however, in agreement with previous studies, we find that Lyt-2+3+ cells are more difficult to depelete with anti-Lyt-1 than Lyt-1+2-3- cells. Surprisingly, we found a small subpopulation of cells carrying relatively large amounts of Lyt-1 and no Thy-1 detectable by fluorescence-activated cell sorter analysis. We also detect cells with this phenotype histologically in B cell zones (primary follicles) and germinal centers in spleen and lymph nodes. In general, the Lyt-1 only population represents approximately 2% of spleen cells. The relative quantitative expression of Thy-1, Lyt-1, Lyt-2, and Lyt-3 changes systematically during T cell maturation. Among Lyt-1+2+3+ cells in the thymus, Thy-1 and Lyt-2 are high, whereas Lyt-1 is low. Among splenic T cells, in contrast, Thy-1 is low, Lyt-1 is high, and Lyt-2 and Lyt-3 are a little higher than in thymus. In general, Thy-1 expression is negatively correlated with Lyt-1. Thus, even among splenic and lymph node T cells subpopulations exist that tend to be either high Thy-1 and low Lyt-1 or vice versa. Lyt-2+3+ cells represent approximately 85% of thymocytes but only approximately 35% of splenic or lymph node T cells. The Lyt-2+3+ cells are found predominantly in the low Lyt-1, high Thy-1 subpopulation.

Care within a veterans hospital: earlier detection of colon cancer.

BACKGROUND: In 1998 the Veterans Administration mandated an externally monitored targeted colon cancer screening rate that was expected to result in earlier cancer detection and improved patient survival. The effectiveness of the protocol was evaluated in a retrospective case series at a tertiary care Veterans Administration Hospital that included all patients with the diagnosis of colon cancer between 1991 and 2003. METHODS: Tumor stage, tumor location, and patient survival data were recorded and compared to National Cancer Data Base (NCDB) benchmarks. RESULTS: The study facility had a greater percentage of early cancers and fewer later stage cancers than the NCDB benchmark. Overall survival was better for the VA cohort compared to NCDB (all-cause 5-year survival: VA, 0.72; NCDB, 0.47. p < or = .001). CONCLUSIONS: The VA facility had a significantly greater percentage of early cancers and fewer stage III or IV cancers compared to a national benchmark and significantly improved survival compared to the national benchmark.

Monoclonal antibodies to a human prostate antigen.

Three monoclonal antibodies reactive with a purified extractable Mr 34,000 prostate antigen (PA) have been prepared by fusing splenocytes of BALB/c mice preimmunized with purified PA with the NS1 mouse myeloma cell line. The three antibodies were all of the IgG-1 subclass. The antibodies defined two noncross-blocking unique determinants on PA; each present as one site per molecule. IF3 defined one antigenic site and 2G7 and 1C5 defined another antigenic determinant. All of the antibodies reacted with PA in a solid-phase radioimmunoassay and immunoprecipitated 125I-labeled PA. Absorption and sandwich radioimmunoassays showed PA in prostate tissues but not in tonsil, liver, or kidney. Immunoperoxidase staining of formalin-fixed paraffin-embedded sections of benign prostatic hyperplasia and prostatic carcinoma revealed strong prostate epithelial reactivity. None of the antibodies showed reactivity with prostate membrane preparations. A sandwich radioimmunoassay used 2G7 as a plate coat. 125I-labeled 1F3 was used to detect 5 ng PA per ml in sera of patients with prostate cancer. These results confirm previous observations regarding the specificity of PA and shed new evidence for its intracellular localization.

Lymphomas presenting as histologically unclassified neoplasms: characteristics and response to treatment.

Malignant lymphoma is frequently diagnosed when immunohistochemical techniques are applied to otherwise unclassified neoplasms. In this analysis of 35 patients with a histologically unclassified neoplasm that expressed leukocyte-common antigen(s) (LCA), actuarial survival was 63%, and 45% of patients were free from disease progression at 30 months following treatment as for lymphoma. The clinical features at diagnosis and the results of combination chemotherapy were found to be similar to a group of patients with a diagnosis of diffuse large-cell lymphoma (DLCL) concurrently treated at this institution. This study further emphasizes the importance of improved diagnostic techniques in the management of histologically unclassified tumors.

Utility of paraffin section immunohistochemistry for C-KIT (CD117) in the differential diagnosis of systemic mast cell disease involving the bone marrow.

Systemic mast cell disease is characterized by an abnormal infiltration of mast cells involving several parenchymal organs and the bone marrow. Its spectrum of clinical and histologic presentation is highly variable and is not necessarily correlated with prognosis. Mast cell disorders presenting as atypical infiltrates in the bone marrow may simulate or be associated with other hematolymphoid malignancies, from which they must be distinguished. The paucity of reliable histochemical and immunohistochemical markers for the detection of mast cells in paraffin sections further confounds this diagnosis. The authors have employed immunohistochemistry for the C-KIT encoded tyrosine kinase receptor protein, CD117, for detection of mast cells on paraffin sections of 89 bone marrow specimens including systemic mast cell disease and other disorders. CD117 staining was found in all cases of mast cell disorders (seven of seven), and in one case of chronic myelogenous leukemia in blast crisis. None of the other myeloid disorders tested (0 of 16), or any of the cases of Hodgkin's disease (0 of 12), B-cell lymphomas (0 of 32), T-cell lymphomas (0 of 3), or histiocytic proliferations (0 of 3) showed staining for CD117. CD117 expression is effective in the separation of mast cell disease from disorders that may simulate it histologically.

Intraepidermal cytokeratin 7 expression is not restricted to Paget cells but is also seen in Toker cells and Merkel cells.

Histologically, extramammary Paget's disease and mammary Paget's disease (MPD) are characterized by large atypical cells distributed throughout the epidermis. Although classic examples of these disorders are easily diagnosed on morphologic grounds, some cases may cause differential diagnostic problems. Immunohistology with a wide variety of antibodies has been used as an aid for the identification of Paget cells, for their distinction from other entities, and for investigation of the origin or nature of the disorder. Recently, cytokeratin 7 has been proposed as a specific and 100% sensitive marker for Paget's disease. We studied 22 cases of mammary Paget's disease and 22 cases of extramammary Paget's disease with and without an underlying malignancy for their reactivity with monoclonal antibodies to cytokeratin 7 (CK7) and cytokeratin 20 (CK20). Our studies show that anti-CK7 is an effective but not 100% sensitive marker for Paget cells, staining 21 of 22 cases of mammary Paget's disease and 19 of 22 cases of extramammary Paget's disease, whereas CK20 stained 0 of 17 cases of mammary Paget's disease and 6 of 19 cases of extramammary Paget's disease. We also demonstrate that CK7, but not CK20, highlights intraepidermal clear cells with bland nuclear features (Toker cells) that have been reported in 11% of normal nipples. By using CK7 as a marker, however, we were able to identify Toker cells in most of the nipples we studied: 8 of 15 nipples from mastectomy patients without Paget's disease, and 15 of 18 autopsy cases (both male and female) with normal breasts and nipples. It also permitted us to perform more extensive phenotyping on them, showing that Toker cells share similar antigens with Paget cells and with cells lining the underlying normal lactiferous ducts. In 7 of 15 cases containing CK20-positive Merkel cells, CK7 was also seen to stain Merkel cells. In infrequent cases, Toker cells or Merkel cells may be so numerous focally that a CK7 stain may raise the possibility of involvement of the nipple by Paget's disease. An awareness of the CK7 reactivity of Toker cells and Merkel cells as well as attention to the cytologic features of the case should avoid this problem.

Atypical fibroxanthoma. Multiple immunohistologic profiles.

The clinical, histologic, and immunohistochemical features of 37 cases of atypical fibroxanthoma (AFX) are presented. Patients ranged in age from 13 to 95 years (mean, 69). Thirty AFXs occurred on the head and neck, and seven lesions developed on the trunk or extremities. The morphologic spectrum varied from a predominant spindle cell pattern with focal cellular pleomorphism to numerous bizarre epithelioid cells with multinucleated giant cells. The spindle cell component in these lesions ranged from 10 to 90% of the constituent cells. Most (31 of 37) AFXs also contained pleomorphic giant cells. Small numbers of S-100-positive dendritic cells were present in 11 cases. Five cases showed variable reactivity with anti-factor-XIIIa. Fifteen (41%) of the AFXs stained for muscle-specific actin or smooth muscle actin and 21 (57%) expressed CD68 (detected with monoclonal KP1), a monocyte-macrophage marker. Reactivity for these antigens was seen in all lesional cell types (spindled, epithelioid, and bizarre). Four immunologic profiles were observed: CD68 only (13 cases), actin only (7 cases), double positives (8 cases), and double negatives (9 cases). No significant differences in staining characteristics were observed in the head and neck versus the trunk and extremity lesions. These results expand the immunohistochemical spectrum of AFX, suggest the concept of heterogenous bimodal "fibrohistiocytic" and "myofibroblastic" phenotypes, and provide further evidence that an integrative, nonalgorithmic approach is necessary in the analysis of these and other spindle cell cutaneous lesions.

Prostatic adenocarcinoma with endometrioid features. Clinical, pathologic, and ultrastructural findings.

Thirteen cases of prostatic adenocarcinoma with endometrioid features were reviewed. The patients were older men (49-81 years) presenting with symptoms of hematuria and urinary obstruction. Each of the tumors displayed exophytic growth into the prostatic urethra, with involvement of the verumontanum. The urethral orifices of the large (primary) prostatic ducts were uniformly involved, and coexistent invasive (acinar) adenocarcinoma was identified in 10 cases (77%). The tumors exhibited a complex glandular pattern strikingly similar to uterine endometrial carcinoma, with prominent papillary formation in six cases. All cases demonstrated intense cytoplasmic immunoreactivity for prostatic acid phosphatase and prostate-specific antigen in at least part of the tumor. Focal staining for carcinoembryonic antigen was seen in three cases. Five tumors examined ultrastructurally demonstrated typical features of prostatic adenocarcinoma. Follow-up information was available on all 13 patients (6-83 months). Seven patients died of metastatic tumor (9-70 months after diagnosis), and the other six patients exhibited recurrent local or metastatic tumor. The sites of metastases were identical to those seen with invasive "acinar" prostatic adenocarcinoma, including pelvic lymph nodes, bones, and lungs. Crude 5-year survival was 15%, with a mean survival of 37 months. Adjuvant therapy provided palliative relief for many patients, but did not appear to influence survival. These findings indicate that endometrioid carcinoma is a histologically distinct variant of prostatic adenocarcinoma, with a more aggressive clinical behavior than previously thought.

Desmoplastic and spindle-cell malignant melanoma. An immunohistochemical study.

The clinical, histologic, and immunohistologic features of 22 desmoplastic melanomas (DMM), 10 mixed desmoplastic and spindle-cell melanomas (DMM/SMM), and two cellular spindle-cell melanomas (SMM) were studied. Patients ranged in age from 35 to 91 years (mean, 67) and included 23 men and 11 women. Seventeen cases occurred in sun-damaged skin of the head and neck. 11 were on the extremities, and six on the trunk. Except for two cases, all were Clark's level IV or V. Twenty-two (65%) cases were associated with a recognizable overlying pigmented lesion. Thirty of 32 (94%) DMM and DMM/SMM were clearly positive for S100. S100 staining was limited to < 5% of the spindle cells in two DMM/SMM. All DMM were negative when stained with HMB45. Three DMM/ SMM were immunoreactive with HMB45, as were both SMM. CD68 staining was limited to < 5% of the spindle cells in two of 32 DMM and DMM/SMM and 20% of the cells in one of two SMM. Nine (32%) DMM and DMM/SMM contained significant numbers of spindle cells immunoreactive for SMA but not desmin. In five cases, the number of actin-positive spindle cells. Two color stains for SMA and S100 demonstrated that these smooth-muscle actin positive cells constituted a separate spindle-cell population, consistent with reactive myofibroblasts. This study indicates that the immunohistologic features of desmoplastic melanoma differ from those of conventional melanoma. If a problematic spindle-cell skin lesion is a suspected melanocytic process, HMB45 is unlikely to provide confirmatory (or exclusionary) evidence for the diagnosis of DMM. Similarly, because of the variability in S100 expression in this neoplasm, the absence of S100 staining should not be relied on too heavily to exclude DMM if the clinical and histologic features favor that diagnosis. Caution should be exercised in the interpretation of numerous actin-positive spindle cells in isolation of additional confirmatory or exclusionary data as desmoplastic melanomas may contain significant numbers of these cells.

Expression of CD34 by solitary fibrous tumors of the pleura, mediastinum, and lung.

Solitary fibrous tumors are rare neoplasms that most commonly involve the pleura, mediastinum, and lung. Because they lack distinctive histologic features, immunologic staining has frequently been employed to exclude other neoplasms in the differential diagnosis. Their reported phenotype to date is generally negative, notably for muscle-type actins, desmin, keratin, and S-100 protein. Although this testing is of some help, it does not serve to distinguish all processes in the differential diagnosis, and when it does, it places too great an emphasis on a negative finding to make a diagnosis. We report here that CD34 monoclonal antibodies reacted with 11 of 14 solitary fibrous tumors in paraffin sections. Thus, they provide a positive marker that distinguishes the solitary fibrous tumor from most elements in the differential diagnosis.

A critical examination of the immunophenotype of pulmonary sclerosing hemangioma.

The authors studied a series of 21 cases of pulmonary sclerosing hemangioma (SH) to address conflicting and unconfirmed reports of immunohistologic evidence of differentiation that have been made in the literature. They found the lesional cells of SH to be epithelial membrane antigen (EMA) positive (21 of 21 cases), to be keratin positive only infrequently and focally (six of 21), and to be nonreactive for carcinoembryonic antigen, S-100, smooth muscle actin, and CD34. Faint nuclear staining was seen for estrogen receptors, whereas progesterone receptors were expressed strongly in 17 cases. Neuroendocrine markers (chromogranin A, adrenocorticotrophic hormone, human growth hormone, and calcitonin) were negative uniformly on the lesional cells except for one case in which rare chromogranin-positive cells were present and another case in which rare human growth hormone-positive cells were seen. In contrast to the general EMA-positive, keratin-negative phenotype of the lesional cells, the cells lining the papillae or air spaces within the SH were typically positive for both markers. The following other lesions were identified in the cases studied: carcinoid tumorlets (n = 2), a neuroendocrine body (n = 1), and multiple meningothelial-like nodules (n = 1). All were clearly separable from the SH on morphologic grounds. The authors interpreted these to be chance occurrences of unrelated lesions. Recognition of the phenotype of SH as EMA positive, keratin weak to negative, and negative for S-100, smooth muscle actin, and neuroendocrine markers is notable in its differential diagnosis from other lesions. This phenotype does not suggest a precise lineage or type of differentiation for SH.

The diagnostic utility of the keratin profiles of hepatocellular carcinoma and cholangiocarcinoma.

A total of 32 hepatocellular carcinomas (HCC), 10 cholangiocarcinomas (CC), one combined HCC-CC, and 10 adenocarcinomas metastatic to the liver were studied immunohistochemically using AE1 and Cam 5.2, monoclonal antikeratin antibodies with different specificities. AE1 recognizes keratins with molecular weights of 56.5, 50/50', 48, and 40 kd (keratin nos. 10, 14, 15, 16, and 19, according to Moll's catalog), and labels many epithelia, including bile duct epithelium, but not hepatocytes. Both biliary epithelium and hepatocytes are stained by Cam 5.2, which reacts with keratins of molecular weights 50, 43, and 39 kd (corresponding to keratin nos. 8, 18, and 19). Tissues were formalin fixed, paraffin embedded, and a three-stage immunoperoxidase technique was employed. Of 32 pure HCCs, 29 were unreactive with AE1 yet were positive with Cam 5.2. The intensity and extent of immunostaining with Cam 5.2 did not correlate with tumor grade. In contrast to the HCCs, all 10 CCs and the 10 hepatic metastases were strongly positive with both AE1 and Cam 5.2. The combined HCC-CC was also labeled by both antibodies. We conclude that most HCCs express an immunohistochemical keratin profile identical to that of nonneoplastic hepatocytes, which differs from the keratin patterns of bile ducts, CCs, and metastatic adenocarcinomas from a variety of primary sites. These differences in immunoreactivity with antikeratin antibodies may prove useful in diagnostic surgical pathology.

Atypical polypoid adenomyofibromas (atypical polypoid adenomyomas) of the uterus. A clinicopathologic study of 55 cases.

We present the clinicopathological and immunohistochemical features of 55 atypical polypoid adenomyofibromas, a definitional expansion of an entity previously reported as "atypical polypoid adenomyoma" (APA) of the uterus. Patients ranged in age from 25 to 73 (mean, 39.9) years. All but two of the patients were premenopausal, and 14 were undergoing evaluation for infertility. Histologically, the lesions featured a biphasic proliferation of architecturally complex and cytologically atypical endometrial glands within a myofibromatous stroma. The histologic pattern ranged from widely separated and loosely clustered irregular but branched glands embedded in broad zones of cellular myofibromatous stroma to those possessing crowded, markedly complex, branching glands separated by sparse intersecting fascicles of fibromuscular tissue. The stroma in all cases was actin or desmin positive or both. Morular/squamous metaplasia was present in all but two cases and florid in most. All cases exhibited architecturally complex glands, and in 25 cases the architectural complexity was indistinguishable from that of well-differentiated endometrial adenocarcinoma, as we have defined it; that is, they had a high architectural index. Twenty-nine patients were initially treated with polypectomy or curettage followed by hormonal therapy; persistent or recurrent APA developed in 45% of the patients in this group (33% with low architectural index vs. 60% with high architectural index). Five patients had successful pregnancies despite persistent disease. Superficial myoinvasion was identified in the hysterectomy specimen in two of 12 APAs with a high architectural index but not in 21 APAs with a low architectural index. All patients are alive and well 1 to 112 months after diagnosis (mean, 25.2 months). On the basis of this study, we propose that APAs with markedly complex glands (high architectural index) be designated "atypical polypoid adenomyofibromas of low malignant potential" (APA-LMP) to emphasize the potential risk for myometrial invasion. A treatment program featuring local excision accompanied by close follow-up is warranted for APA despite the presence of recurrent or persistent disease. Patients with APA-LMP may also, in selected cases, be managed with less than hysterectomy, although (as with the usual well-differentiated carcinoma) there is a small but definite risk associated with this approach.

Esophageal submucosal gland duct adenoma.

An 81-year-old man with a 3-year history of dysphagia underwent endoscopic resection of a 1-cm-diameter distal esophageal mass. Examination revealed a submucosal neoplasm with a circumscribed growth pattern composed of tubules, cysts, and papillae in association with a marked interstitial lymphoid infiltrate. The cyst lumens and papillae were lined by two to six layers of cytologically bland cuboidal to columnar cells with rare mitotic figures. The basal layer of cells was uniformly positive for smooth-muscle actin. Mucin-positive intracytoplasmic lumens were focally present, but cytoplasmic mucin was not seen. There was no evidence of Barrett's metaplastic epithelium. These features are similar to those in two, possibly three, previously reported cases of esophageal adenomas and bear a resemblance to sialadenoma papilliferum, a rare neoplasm of the minor salivary glands. Their clinicopathologic and immunohistologic features suggest that these neoplasms derive from the submucosal gland ducts. Comparison with the previously reported cases indicates that although the proportions of the various components (tubules, cysts, and papillae) may vary, all cases appear to pursue a slowly growing, clinically indolent course with no evidence of recurrence after complete resection.

Study of murine T cell migration using the Thy-1 allotypic marker. Demonstration of antigen-specific homing to lymph node germinal centers.

We describe the use of Thy-1 alloantigen as a marker for in vivo T lymphocyte homing studies. Following transfer of 5 x 10(7) peripheral node T cells i.v., 32% of the transferred cells could be recovered in the host lymphoid organs (spleen, lymph nodes, Peyer's patches, and thymus); 11% of the T cells in the lymph nodes were donor derived. The transferred T cells assume the same microenvironmental and immunophenotypic distribution as the host T cells. The transferred T cells are identifiable in peripheral lymph nodes up to 170 days posttransfer, gradually declining in number during this time without evidence of rejection. This Thy-1 transfer technique permits T lymphocyte homing studies to be performed under physiologic conditions without problems of loss of lymphocyte subsets, selective labeling of lymphocyte populations, or long-term marker loss or dilution. We then employ this technique to demonstrate the antigen-directed homing of peripheral T cells to lymph node germinal centers.

Expression of major histocompatibility complex antigens in the thymuses of chimeric mice.

Thymuses of various types of bone-marrow-chimeric mice have been examined by tissue section immunologic staining for the presence and distribution of major histocompatibility complex (MHC) antigens. Cortical and medullary thymic epithelial cells continue to express thymus genotype I-A and H-2K/D antigens for at least 6 months posttransplantation. The appearance of bone-marrow-type MHC antigens is limited to low levels of H-2K/D on cortical and medullary lymphocytes, and to dendritic cells in the medulla; the medullary dendritic cells express high levels of donor-type I-A antigens as soon as 3 weeks posttransplantation. The observed patterns support the concept that I-A antigens are synthesized by thymic epithelial cells but are acquired by thymocytes. The findings are of relevance to the understanding of the role of the thymus in the generation of MHC restriction.

Distribution of H-2 microenvironments in the mouse thymus. Immunoelectron microscopic identification of I-A and H-2K bearing cells.

Antigens coded for by the major histocompatibility complex (MHC) are differentially expressed in the mouse thymus. Immunoperoxidase studies of frozen thymus sections incubated with monoclonal (hybridoma) anti-I-Ak antibodies revealed a dendritic straining pattern in the cortex and a confluent staining pattern in the medulla. Serial sections incubated with monoclonal anti-H-2Kk antibodies showed that H-2Kk antigens were only present at detectable levels in the medulla. Microenvironments expressing H-2Kk antigens also expressed I-Ak antigens. In cortico-medullary regions, relatively large MHC-negative areas were found. These areas appeared to connect to perivascular spaces surrounding blood vessels. Using a new postfixation labeling method for the detection of cell surface associated antigens on cells of the lymphoid system in situ, we have characterized the nature of MHC positive cell types at the ultrastructural level. These studies show that epithelial-reticular cells are the major MHC positive elements in the thymus. Lymphocytes in the medulla and in cortico-medullary bounderies are also MHC positive, however, lymphocytes in the cortex were not detectably labeled. These findings support the contention that epithelial-reticular cells are involved in the H2-restriction process during T cell maturation.

Monoclonal antibodies reactive with subsets of mouse and human thymic epithelial cells.

We describe monoclonal antibodies (MAB) reactive with subsets of mouse and human thymic epithelial cells. Rat MAb CDR1 reacts with mouse but not human cortical epithelial cells. Immunologic staining of thymic nurse cells in suspension indicates the CDR1 antigen is located on the cell surface. Mouse MAb CDR2 reacts with human but not mouse cortical thymic epithelial cells. Rat MAb MD1 and MD2 detect different determinants expressed by most medullary epithelial cells in mouse thymus but fewer such cells in human thymus. In addition, MD1 detects flattened subcapsular cells rarely in mouse thymus but frequently in human thymus. Two-color stains using an anti-keratin antiserum demonstrate the epithelial nature of the cells reactive with these antibodies. The antigens detected by CDR1 and MD1 first appear during the neonatal period, achieving adult distribution by postnatal days 14 and 4, respectively. The extra-thymic staining of these MAb is described. On the basis of their intra- and extra-thymic reactivities, these MAb differ from those previously reported and may permit dissection of the thymic microenvironment.