Macrophage-associated Antigens Research Articles

Reduced expression of macrophage-associated antigens on alveolar mononuclear phagocytes from acquired immunodeficiency syndrome.

In this study we evaluated the phenotype of alveolar mononuclear phagocytes recovered from the bronchoalveolar lavage fluid of 24 patients with human immunodeficiency virus infection (AIDS-related complex 8 patients. AIDS 16 patients) and 8 healthy individuals by using a panel of monoclonal antibodies known to react with tissue macrophages, in combination with a flow cytometer. The results showed that 90% of patients with AIDS present a marked reduction in the expression of several antigenic determinants (in decreasing order: CD68, CD36, CR1, CD11c, HLA-DR). The levels of antigen expression by flow cytometry seem to decline with disease progression, showing the most dramatic perturbations in patients with full-blown AIDS associated with pulmonary infections (especially Pneumocystis carinii pneumonia) and lower peripheral CD4 lymphocyte counts. In contrast, patients with AIDS-related complex or AIDS without histological or cultural evidence of pulmonary involvement showed, respectively, only minimal or medium antigenic decreases. However, only a minor proportion (16%, 20%, 20%, 25%, and 25% respectively) of human immunodeficiency virus infected patients (mostly with AIDS) had a significant reduction of the levels of CD4, CD14, CD45R, CD11b, and CD16 antigens in the alveolar macrophages. Since macrophages play a central role in the pathogenesis of AIDS, it may be postulated that the loss of various phenotypic markers on alveolar mononuclear phagocytes (some of them known for their important immunoregulatory actions) could have an important part in the pathogenesis of human immunodeficiency virus induced immunosuppression, and thereby condition the abnormal susceptibility to pulmonary diseases typical of human immunodeficiency virus-infected patients.

Immunophenotypic Analysis of Mononuclear Phagocyte Antigens in the Arthritic Synovium of the Hip Joint

The antigenic phenotype of lining and subintimal mononuclear phagocytes (MPs) of the synovium in osteoarthritis (OA) and rheumatoid arthritis (RA) was characterised, using monoclonal antibodies directed against a range of monocyte/macroph-ageassociated antigens, in order to determine the role of MPs in the pathobiology of OA and RA of the hip. A major proportion of synovial lining cells (SLCs) and subintimal cells in RA and OA consisted of CD68 positive MPs which expressed a wide range of macrophage-associated antigens. The monocyte marker, CD14, was downregulated on SLCs in RA while OA and early markers of MP activation predominated in the OA synovium which was independent of the level of inflammation. In contrast, synovial MPs in RA showed increased expression of activation, maturation and functional antigens such as CD11a, CD11b, CD11c, CD16, CD32, CD54, CD64. Moreover, MP recruitment did not correlate with the degree of lymphocytic infiltration in RA. Thus, synovial MPs in RA are rapidly and fully activated with upregulation of activation, differentiation, and functional antigens occurring in situ. There was also no difference in antigenic phenotype of synovial MPs in inflammatory and non-inflammatory OA.

Extracellular matrix in hepatoblastoma: an immunohistochemical investigation.

Eleven hepatoblastomas of various subtypes and normal liver tissue were investigated with antibodies against collagen types I-VI, laminin, fibronectin and endothelial and macrophage-associated antigens. Epithelial hepatoblastoma cells, unlike non-neoplastic hepatocytes, exhibited intracellular immunoreactivity for various extracellular matrix proteins (depending on the subtype: laminin, fibronectin and collagen types III, IV and V). The intracellular expression of extracellular matrix proteins by the tumour cells increased from the fetal subtype, through the embryonal subtype, to the small cell subtype. The epithelial tumours exhibited sinusoid-like blood vessels in numbers that varied according to the subtype. These contained Kupffer cells and exhibited greater amounts of the basement membrane components collagen type IV and laminin in the perisinusoidal space than those in the normal liver. The small cell hepatoblastoma exhibited smaller numbers of sinusoids, pronounced intracellular expression of extracellular matrix proteins and large numbers of fibres immunoreactive for collagen type III. In the mixed hepatoblastomas, the extracellular matrix of the osteoid was most strongly immunoreactive for collagen type I and that of the spindle cell areas for collagen type III.

Immunophenotypic differences between osteoclasts and macrophage polykaryons: immunohistological distinction and implications for osteoclast ontogeny and function.

The antigenic phenotype of human fetal osteoclasts was compared with that of human tissue macrophages and macrophage polykaryons in foreign body lesions using a large number of monoclonal antibodies directed against myeloid (granulocyte/mononuclear phagocyte) antigens. Osteoclasts expressed a restricted range of macrophage-associated antigens including CD13, CD15A, CD44, CD45, CD54, (ICAM-1), CD71 (transferrin receptor), and CD68. These antigens were also present on macrophages and macrophage polykaryons both of which also strongly expressed CD11a,b,c, CD18, (LFA family), CD14, CD31, CD36, CD37, CD39 and CD43 antigens. There was also weak and occasional expression of CD16 (FcRIII), CD25 (interleukin 2 receptor), CD32 (FcRII), CD35 (C3b receptor) and HLA-DR by macrophage polykaryons. The presence of some macrophage associated antigens on osteoclasts is consistent with their originating from cells of the mononuclear phagocyte system. The numerous differences in antigenic phenotype between osteoclasts and macrophage polykaryons, however, suggest that their pathways of development and differentiation are not identical. The differences discerned in antigenic phenotype should also permit distinction between these polykaryons (and possibly their mononuclear precursors) in normal and diseased tissues.

Immunohistochemical demonstration of leucocyte differentiation antigens on paraffin sections using a modified AMeX (ModAMeX) method.

The AMeX method (cold Acetone fixation with subsequent Methyl benzoate and Xylene treatment and routine paraffin embedding) has been recently revived for simultaneous preservation of morphology of cells and their antigens. We propose a modification of this method (ModAMeX), with the use of proteolytic enzyme inhibitors and low temperature paraffin wax embedding, which results in better preservation of a large number of leucocyte differentiation antigens and diagnostic morphologic detail. T-cell antigens (CD1, CD2, CD3, CD7 & CD8), B-cell antigens (CD22), macrophage associated antigens (CD11c, CD14 and others), activation antigens (CD25 and others), as well as some other antigens of diagnostic interest (CD10) were found to be preserved with a staining intensity equal to that of sections of fresh frozen tissue. Although the staining intensity of other T-cell antigens (CD4 & CD5), B-cell antigens (CD19, CD21 & CD37), activation antigens (Ki-1) and nuclear proliferation antigen (Ki-67) was slightly weaker as compared with frozen sections, this could be corrected by increasing the monoclonal antibody concentration. Staining for heavy and light chains of immunoglobulins was minor, sometimes compromised due to persistence of background staining as a result of extracellular immunoglobulins. The ModAMeX method has the advantages of simplicity, low cost and the possibility of exchange of tissue material between laboratories.

Expression of Macrophage-Associated Antigens in Tissues Involved by Langerhans’ Cell Histiocytosis (histiocytosis X)

The expression of macrophage antigens KP1, Mac, lysozyme, and alpha-1-antichymotrypsin was investigated on routine paraffin sections from 17 cases of Langerhans' cell histiocytosis (LCH). All the major clinical forms were represented, including single lesions and monosystemic and multisystemic disease. In all the cases, a variable fraction (3-35%) of LCH cells was immunoreactive with KP1 and anti-Mac; the staining pattern was quite typical because the immunoreaction product was often confined to the perinuclear space and the Golgi area. LCH cells containing lysozyme and AACT were detected less frequently; however, in positive cases the percentage of LCH cells immunoreactive for lysozyme and AACT was in the same range as that of KP1-positive cells. On immunostained cytosmears (one case), about 10% of the CD1a-positive cell population was reactive for the macrophage antigens CD14 and PAM-1. No association was noted between the number of KP1-positive cells and the clinical form and/or anatomic site of the lesion. Phagocytic macrophages were significantly and diffusely immunoreactive with KP1 and anti-Mac and for AACT and lysozyme. Multinucleated giant cells with irregular nuclei were frequently observed; these cells were rarely S-100 positive, were consistently stained by KP1 and AACT, and were occasionally anti-Mac positive. The authors' findings suggest that antimacrophage monoclonals, in conjunction with S-100 protein, may represent a useful tool to establish the diagnosis of LCH in paraffin-embedded material.

Microglia in the neurohypophysis associate with and endocytose terminal portions of neurosecretory neurons

The rat neurohypophysis contains a population of microglial cells, the majority of which occupy a pericapillary position in the resting gland. The microglia are immunocytochemically identifiable by the presence of macrophage-associated antigens and resemble microglia of the CNS. Morphometry at light and electron microscopic levels reveals that such cells constitute approximately 19% of the intrinsic cell population, excluding the endothelial cells. Two other populations of neurohypophysial glial cells, parenchymatous pituicytes and fibrous pituicytes, do not express macrophage-associated antigens. The microglia have long processes which surround and, in some cases, engulf apparently viable portions of the magnocellular neurosecretory nerve terminals. A sequence of stages of selective endocytosis and degradation of the engulfed nerve terminals can be visualized within pericapillary microglia. Some phagosomes and secondary lysosomes contain morphologically intact neurosecretory granules; others contain partially destroyed neurosecretory granules or amorphous material all of which are identifiable as originating from the magnocellular neurosecretory terminals by their immunoreactivity for oxytocinor vasopressin-neurophysin. This finding indicates a novel role for the microglial cells in remodelling terminal arborizations of neurosecretory neurons and in processing or degrading hormones and peptides they contain. Because of their close and selective associations with other cellular elements of the neurohypophysis, any substances produced by microglia also have the potential to influence hormone secretion, pituicyte proliferation and neurohypophysial vasculature.

Chondroblastoma: An immunohistochemical study

Five chondroblastomas were examined for the presence of monocyte/macrophage-associated antigens by an alkaline phosphatase-anti-alkaline phosphatase immunohistochemical method. The tumor cell populations were analyzed with eight antibodies reacting with separate antigens on cells of monocyte/macrophage lineage and with antibodies directed against glycoprotein IIIa and factor VIII. The "chondroblastic" tumor cells did not stain with any of the macrophage-associated antibodies. Osteoclast-like giant cells stained with the macrophage-associated antigens EBM11, KB90, leukocyte common antigen, and with the megakaryocyte/platelet-associated antigen C17. Only endothelial cells were reactive with antibody to factor VIII. Our data do not support the postulated histiocytic origin of the neoplastic cells within chondroblastomas; the osteoclast-like giant cells present within these tumors are felt to be both reactive and of monocyte/macrophage lineage.

An investigation into the nature of giant cells in cardiac and skeletal muscle

In an immunohistochemical study of six cases of giant cell myocarditis, the typical giant cells have been shown to express up to four different macrophage-associated antigens, but not desmin, the intermediate filament protein characteristic of muscle cells. These results support the view that the giant cells have a macrophage rather than a myogenic origin. In contrast, the giant cells found in regenerating skeletal muscle have the immunophenotype of muscle cells and not of macrophages supporting their muscle origin.

Expression of lymphoid-associated antigens on Hodgkin's and Reed-Sternberg cells of Hodgkin's disease. An immunocytochemical study on lymph node cytospins using monoclonal antibodies.

The aim of this study was to elucidate the origin of Hodgkin's and Reed-Sternberg cells. Lymph node cytospins and frozen sections from 20 cases of Hodgkin's disease of different histological subtypes were immunostained by the immuno-alkaline phosphatase technique using a panel of monoclonal antibodies. As expected, the Hodgkin's and Reed-Sternberg cells of all cases were positive for the CD30 (Ki-1), CD15 (hapten X) and CD25 (Tac) antigens. In eight cases, a variable percentage of typical Hodgkin's and Reed-Sternberg cells showed a clear-cut cytoplasmic and/or surface positivity for the T-cell-associated antigens CD3, CD5, CD6 and CD4 (seven cases) or CD8 (one case), but consistently lacked B-cell and macrophage-associated markers. The best visualization of T-cell antigens was obtained in cytocentrifuge preparations and in areas of lymph node frozen sections that had been infiltrated by clusters of Hodgkin's and Reed-Sternberg cells. In two cases of Hodgkin's disease (nodular sclerosis, mixed cellularity) the neoplastic cells weakly expressed the B-cell antigens CD19 and CD22, but not T-cell or macrophage-associated markers. In 10 cases, Hodgkin's and Reed-Sternberg cells were negative for all the lymphoid- and macrophage-associated antigens. These results suggest a lymphoid (either T or B) rather than histiocytic origin for the Hodgkin's and Reed-Sternberg cells in a number of Hodgkin's disease cases.

Histiocytic necrotizing lymphadenitis without granulocytic infiltration (Kikuchi's lymphadenitis). Morphological and immunohistochemical study of eight cases.

Eight examples of histiocytic necrotizing lymphadenitis without granulocytic infiltration (Kikuchi's lymphadenitis) are described. They occurred in young or middle-aged women who usually complained of latero-cervical lymphadenopathy. Serology revealed significant titres for Epstein-Barr virus and Yersinia enterocolitica serogroup 9 in one of eight and one of six tested. All patients fully recovered within 2 months. On histological examination of the lymph nodes large foci of infiltration were observed in the cortex and/or paracortex: they consisted of variable numbers of small lymphocytes, immunoblasts, macrophages and so-called plasmacytoid T-cells; granulocytes were absent. Necrotic changes varied from single pyknotic cells to extensive areas of necrosis. Immunohistochemistry showed that within the lesion the number of macrophages was inversely proportional to the number of peripheral T-lymphocytes and 'plasmacytoid T-cells'. The latter displayed a phenotype (CD4+, CD10+, CD45+) which, in the absence of macrophage-associated antigens, seemed in keeping with their supposed lymphoid nature. In seven cases peripheral T-lymphocytes predominantly expressed the cytotoxic/suppressor phenotype, while in one remaining case a mild predominance of the helper/inducer subset was observed. In the areas with less extensive tissue necrosis, numerous T-immunoblasts expressed both markers of activation and the proliferation-associated nuclear antigen Ki-67. The results of the present study expand the spectrum of our knowledge and allow speculation as to the biology of this disease.

Sequential immunophenotypic study of lymphoid infiltrate in allergic and irritant reactions.

Sequential biopsies (4-72 h) of early allergic and irritant patch test reactions have been examined immunohistologically for reactivity with 19 monoclonal antibodies against antigens on lymphoid cells in order to investigate the nature/origin of the infiltrating lymphoid cells and assess their state of activation/proliferation. The composition of the infiltrates was similar in allergic and irritant reactions and consisted of T-lymphocytes of helper/inducer types in association with T-cell accessory cells, i.e., Langerhans cells and HLA-DR-positive macrophages. No differences in expression of T-cell or macrophage associated antigens were seen in early as opposed to late biopsies. In contrast, the proportion of cells positive for markers associated with activation (interleukin-2 receptor) or proliferation (transferrin receptor, the Ki-67 nuclear antigen) of lymphoid cells was found to increase with time in both types of reaction. These data substantiate the view that T-cell immune reactions are implicated in both allergic and toxic patch test lesions, and indicate that the lymphocytes in the infiltrates are activated and proliferate.

Osteoclasts contain macrophage and megakaryocyte antigens.

The origin and mechanism of formation of the osteoclast remains controversial. Although it is known to be derived from a circulating mononuclear percursor, the identity of this cell is unknown. Using a panel of monoclonal antibodies raised against macrophage and other marrow-derived cells, we determined the immunocytochemical staining of human osteoclasts in both fetal bone metaphyseal imprints and frozen sections. Osteoclasts and marrow mononuclear cells were stained by three broad spectrum antimacrophage antibodies, EBM-11, Y182a and BM2. T310, an antibody which stains macrophages and T helper cells, and C17, an antimegakaryocyte antibody, also stained osteoclasts. EBM-11, Y182a and BM2 also stained megakaryocytes in bone imprints as well as normal bone marrow smears. The presence of macrophage-associated antigens in osteoclasts, megakaryocytes and bone marrow mononuclear cells indicates that they are phenotypically similar to macrophages.

Absence of Mononuclear Phagocyte Antigens in Malignant Fibrous Histiocytoma

Nine malignant fibrous histiocytomas (MFHs) were tested for the presence of macrophage-associated antigens by an alkaline phosphatase-anti-alkaline phosphatase immunohistochemical method. One myxoid and eight pleomorphic-storiform tumors were analyzed with eight antibodies reacting with separate antigens previously found on cells of mononuclear phagocyte lineage. Malignant cells did not react with any of the antibodies, while benign histiocytes within tumor were consistently labeled with all of the antibodies tested. While the malignant cells of MFH previously have been found to share some functional and morphologic properties with histiocytes, they do not possess the surface and cytoplasmic antigens that have been found on various macrophage populations. The malignant cells of MFH are fibroblastic or poorly differentiated mesenchymal cells rather than neoplastic histiocytes.

Identification and molecular characterization of macrophage-associated antigens of the rat.

Rabbit antiserum to rat peritoneal exudate (PE) macrophage (M phi) antigens was prepared and its reactivity with cell surface proteins of M phi, granulocytes, and lymphocytes was studied by one- and two-dimensional polyacrylamide gel electrophoresis (PAGE). A total of 14 membrane antigens were identified of which three were found to be expressed only by M phi and granulocytes. By one-dimensional analysis, a protein with an approximate m.w. of 105,000 was present on splenic and PE M phi and on splenic lymphocytes. Two-dimensional analysis revealed that this band was heterogeneous and contained at least three species, one of which was restricted to expression on M phi and granulocytes. A second protein of 150,000 daltons was resolved into two species by two-dimensional analysis. Both of these species were present on M phi and granulocytes but not on lymphocytes. Both the 105,000- and 150,000-dalton proteins were glycosylated. Because the 105,000- and 150-000-dalton proteins expressed by M phi were also expressed by granulocytes, is is likely that these are differentiation antigens whose expression is a characteristic property of cells within both monocytoid and myeloid lineages. All three 105,000-dalton species and one of the two 150,000-dalton species were detected on mouse M phi, indicating their expression is not unique to the rat.

Nature of T lymphocyte recognition of macrophage-associated antigens: III. Definition of the antigenic regions of human fibrinopeptide B involved in guinea pig T-cell responses

The clonal diversity of guinea pig T-lymphocyte responses to the 14-amino-acid peptide antigen human fibrinopeptide B (hFPB, Bβ1–14) and sequential hFPB 3 3 Abbreviations used: hFPB, human fibrinopeptide B; [ 3H]TdR, [methyl- 3H]thymidine; Ia, I region-associated antigens; NGPS, normal guinea pig serum; PPD, purified protein derivative of tuberculin; BUdR, bromodeoxyuridine; CFA, complete Freund's adjuvant; PEL, peritoneal exudate lymphocyte. homologs (Bβ5–14 and 7–14) was examined using bromodeoxyuridine (BUdR) and light elimination of T cell responses. PPD and hFPB-immune strain 2 guinea pig T cells and macrophages were stimulated in a first culture with PPD, Bβ1–14, 5–14, or 7–14; BUdR was added on the second day and the cultures exposed to light on the third day. The BUdR and light-treated T cells recovered from the first culture were restimulated in a second culture containing fresh stimulator macrophages and PPD, Bβ1–14, 5–14, and 7–14. BUdR and light-treated T cells initially stimulated with Bβ1–14 in the first culture showed no responsiveness to Bβ1–14, 5–14, or 7–14 in the second culture. BUdR and light-treatment of T cells initially stimulated with Bβ5–14 eliminated 70 to 80% of the subsequent response to Bβ1–14 and all of the responsiveness to Bβ7–14. Similar treatment of T cells stimulated with Bβ7–14 reduced responsiveness to Bβ1–14 by 50 to 60% and to Bβ5–14 by 60 to 70%. These observations indicate that T-cell responses are directed against three antigenic regions in the hFPB molecule; the major region defined by the carboxy-terminal sequence including residues 7 to 14, a second minor antigenic region including residues 5 and 6, and a third minor region including the amino terminal residues 1 to 4. Results are discussed with respect to the regions of the hFPB molecules that are recognized by antigen-binding T-cell receptors and the regions which interact with stimulator macrophages.

The Regulatory Role of Macrophages in Antigenic Stimulation Part Two: Symbiotic Relationship between Lymphocytes and Macrophages

Publisher Summary Changes in antigen molecules that resulted in enhanced or decreased uptake by the phagocytes resulted in higher or lower immune responses, respectively. After the development of methodologies for obtaining live exudate cells rich in phagocytes and for pulsing these with antigen, the immune response to macrophage-associated antigens was possible to assay, using combinations of in vivo and in vitro methods. The presentation of antigen bound to live macrophages to the lymphocytes was a highly efficient mode of generating an immune response. In the marine system, the requirement for phagocytes or other acc|essory cells was such that as little as 1% contamination with phagocytes still enabled a T-cell proliferative response to develop. Thus, depletion procedures had to be extremely efficient. Macrophages are definitely involved in some response to many of the conventional polyclonal stimuli. Involvement of the macrophage may be by way of secreted active molecule. Fc fragments of Ig act as a polyclonal stimulant only after a processing of the fragment by the macrophages. The developments in macrophage biology over the past few years were not predicted till 1972.

Nature of T lymphocyte recognition of macrophage-associated antigens. IV. Inhibition of peptide antigen presentation by brief treatment of macrophages with anti-Ia serum

To examine the role of macrophage la antigens in T-lymphocyte stimulation, guinea pig macrophages were briefly treated with anti-Ia serum before or after antigen pulsing with the peptide antigen human fibrinopeptide B (hFPB). To assess their antigen-specific stimulatory capacity, the variously treated macrophages were added to culture with hFPB-immune guinea pig T cells and stimulation was determined by the incorporation of [ 3H]thymidine. Macrophages treated with anti-Ia serum before antigen pulsing stimulated T-cell responses equivalent to those observed with antigen-pulsed macrophages treated with normal serum. By contrast, brief anti-Ia treatment of macrophages immediately following a 2-hr antigen pulse reduced subsequent T-cell responses by 45 to 70%. Similar treatment of macrophages pulsed with antigen for only 1 hr produced only modest inhibition of T-cell responses. However, if macrophages pulsed for 1 hr with antigen were incubated several hours before brief anti-Ia serum treatment, the subsequent T-cell responses were reduced by 40 to 60%. This inhibition was specific for antiserum directed against Ia antigens of the guinea pig MHC, since brief macrophage treatment with antiserum directed against B.1 antigens, the guinea pig equivalent of murine H-2K and H-2D antigens, produced no inhibition of their T-cell stimulatory capacity. These results are discussed with respect to the formation of the immunogen presented by macrophages for T-cell recognition.

Nature of T lymphocyte recognition of macrophage-associated antigens. V. Contribution of individual peptide residues of human fibrinopeptide B to T lymphocyte responses.

Guinea pig T lymphocyte responses to a decapeptide antigen (NH1-Asp5-Ans6-Glu7-Glu8-Gly9-Phe10-Phe11-Ser12-Ala13-Arg14-OH) of human fibrinopeptide B (hFPB) were examined using various synthetic peptide analogues containing single residue substitutions. Each analogue was examined for antigenicity as determined by an in vitro proliferative responses of hFPN-immune strain 2 guinae pig T cells. In addition, both strain 2 and strain 13 animals were immunized with each analogue and immunogenicity assessed by in vitro T cell-proliferative responses with the homologous immunizing analogue and the parent peptide. Replacement of arginine14 with lysine formed an immunogenic analogue which showed no antigenic cross-reactivity with the native peptide in strain 2 T cell responses. In addition, substitution of arginine14 with blocked lysine again produced a unique immunogenic analogue that showed little or no antigenic identity with the intact lysine analogue or the native peptide. In similar fashion, substitution of resideu phenylalanie10 with tyrosine or Phe(4-NO2) created unique immunogenic analogues with little or no antigenic identity to the native peptide with strain 2 T cells. By contrast, replacement of phenylalanine11 with either tyrosine or Phe(4-NO2) resulted in analogues with a total loss of immunogenicity and antigenicity in strain 2 T cell responses. An analogue in which glutamic acid7,8 were replaced with glutamine retained a small degree of antigenicity with hFPB-immune T cells, but T cells from strain 2 animals immunized with the Gln analogue responded only marginally to the Gln analogue while producing good proliferative responses with the native peptide. On the other hand, an analogue in which asparatic acid5 was replaced with asparagine retained most of the antigenic identity with hFPB for strain 2 T cell responses. None of thee analogues were immunogenic for strain 13 guinea pigs. These observations are discussed with respect to the contribution of each substituted residue to T cell respones, mechanism of Ir gene function, and a model for T cell recognition of small peptide antigens.

Nature of T Lymphocyte Recognition of Macrophage-Associated Antigens

Abstract Strain 2, strain 13, or (2 × 13)F1 guinea pigs were immunized with human fibrinopeptide B, a 14 amino acid thrombin-derived fragment of the Bβ chain of fibrinogen (Bβ1-14), or the Bβ1-13 homologue, and in vitro T lymphocyte responsiveness was determined by the incorporation of 3H-thymidine. T cells from strain 2 or (2 × 13)F1 animals immunized with Bβ1-14 showed proliferative responses with Bβ1-14 but were unresponsive with Bβ1-13. Bβ1-13, Strain 13 Bβ1-14 immune T cells were unresponsive with both Bβ1-14 and 1–13. By contrast, T cells from strain 13 or (2 × 13)F1 guinea pigs immunized with Bβ1-13 produced proliferative responses with Bβ1-13 but not with Bβ1-14. Strain 2 Bβ1-13 immune T cells showed minimal or no responsiveness with Bβ1-13 or 1–14. Thus, responsiveness to Bβ1-14 is associated with strain 2 animals, and responsiveness to Bβ1-13 is associated with strain 13 guinea pigs. To determine the role of macrophages in presentation of Bβ1-14 or 1–13, T cells from (2 × 13)F1 guinea pigs immunized with Bβ1-14 or 1–13 were stimulated by antigen in association with macrophages derived from either parent. F1 T cells immunized with Bβ1-14 responded to Bβ1-14 in association with only strain 2 but not strain 13 macrophages. By contrast, Bβ1-13 immune F1 T cells responded with Bβ1-13 in association with only strain 13 but not strain 2 macrophages. These results are discussed with respect to the role of macrophages in selecting immunogenic determinants of peptide antigens for presentation to T cells.