FC receptor for IgM: factors influencing detection on human T lymphocytes

Dissociation between coupled lymphocyte phenotypic and functional properties in Sézary cells

Neoplastic lymphocytes derived from three patients suffering from Sézary syndrome were studied by immunologic and functional analysis. Populations of neoplastic T cells (greater than 90% as judged by morphologic criteria) were isolated from involved lymph nodes. Sézary cells expressed T3 and T4 but not T8 membrane antigens displaying the same phenotypic pattern of normal helper/inducer T cells. On the contrary the mitogenic response of Sézary cells to phytohemagglutinin appears lower than that exhibited by peripheral T lymphocytes. The amounts of interleukin 2 produced by Sézary cells were examined in two out of three cases: in one case it appeared similar to that produced by peripheral blood lymphocytes while in the other it was about one-half lower. Furthermore the capacity of dexamethasone at 10(-7) M in inhibiting T-cell mitogenesis was comparatively analyzed in T lymphocytes from Sézary lymph nodes, reactive lymph nodes, normal peripheral blood, and normal thymus. It was clearly apparent that the mitogenesis of Sézary cells, unlike that of peripheral blood lymphocytes and that of lymphocytes from reactive lymph nodes, was strongly inhibited by dexamethasone (greater than 70%); such inhibition was very similar to that observed for normal thymocytes. Taken together these results suggest that despite the phenotypic pattern of mature helper/inducer T cells, Sézary lymphocytes are functionally a less mature T-cell type.

A human thymoma with prothymocyte-like infiltration

We have examined a human thymoma, round-oval epithelial-type cell with moderate lymphocytic infiltration, whose major lymphocytic component (67%), unlike the minor one (33%), did not form rosettes with sheep red blood cells (E rosettes). However, these cells were of T-cell nature as indicated by the positive staining for both acid phosphatase and beta-glucuronidase, two well-accepted cytochemical markers for T cells. The non-E-rosetting lymphocytes expressed T 10, but not T 3 and T 6 antigens. Moreover, they lacked both peanut agglutinin and Fc-IgG receptors. On the contrary, 71 and 19% of the E-rosetting cells were PNA- and Fc-IgM-receptor positive, respectively. Furthermore, the non-E-rosetting cells were phytohemagglutinin unresponsive. The non-E-rosetting lymphocytes were larger (greater than 7 micron) than the E-rosetting cells and showed a different nuclear chromatin pattern. These immunological, cytochemical, and morphological features strikingly resemble those exhibited by cells (prothymocytes) normally found only in fetal thymus. On the basis of these findings we hypothesize the existence in this thymoma of a prothymocyte-like infiltration.

Human thymoma lymphocyte mitogenesis: glucocorticoid inhibitory capacity as a function of the size of the more mature T cell subset

The relationship between the expression of T3 and T6 antigens and the capacity to respond to phytohaemagglutinin (PHA) has been studied in the lymphocyte component of nine human thymomas. It appears that there is a positive correlation between the mitogen responsiveness of thymoma lymphocytes and the relative proportion of T3 positive (T3+), T6 negative (T6-), peanut receptor negative and IgM-Fc receptor positive cells. Moreover we have comparatively investigated the dexamethasone (Dex) inhibitory effect on the mitogenesis of T lymphocytes from thymoma, normal thymus and peripheral blood. In the presence of the macrophage product interleukin 1, the capacity of Dex to inhibit the mitogenesis of peripheral blood purified T cells (PBT) is inversely correlated with the PHA concentration used. Conversely, Dex completely (greater than 90%) inhibits thymocyte mitogenesis irrespective of PHA concentration. The entity of Dex inhibitory effect on thymoma lymphocyte mitogenesis shows a great variability ranging between that observed in normal thymocytes and that observed in PBT. In each thymoma case the degree of inhibition appears to be dependent on the size of the more mature thymocyte pool being positively correlated with the number of T6+ but negatively with that of T3+ cells. Our data demonstrate a high degree of variability among thymomas relative to the phenotypic and functional properties of their lymphocytic component. On the other hand, in some thymomas the phenotypic and functional characteristics of lymphocyte component seem to represent only a narrow span of normal thymocyte maturative pathway. In this respect, human thymoma may constitute a profitable tool for studying the intrathymic T lymphocyte maturative steps.

Imbalances in peripheral blood T-cell subpopulations in renal transplant patients

The distribution of T-lymphocyte subpopulations bearing receptors for the Fc portion of IgG (TG) or IgM (TM) was monitored in 22 renal allograft recipients treated with immunosuppressive therapy and in 10 uraemic patients on haemodialysis. No significant difference in the distribution of T cells and T-cell subsets was found between normal controls and haemodialysed patients. In transplanted patients, however, a significant reduction of the total T-cell percentage (P less than 0.005), of TM subset percentage (P less than 0.025) and absolute number (P less than 0.005) and of TG absolute number (P less than 0.05) was observed. Considering patients with allografts functioning for more than 1 year only, the reduction in TM cells in terms of percentage (P less than 0.0005) and absolute number (P less than 0.025) was significant, while TG subset levels did not change significantly. In patients transplanted less than 1 year previous to our study, total T cells and T-cell subsets were reduced significantly only as absolute numbers. During the 1st year we observed several increments of TM values towards normal levels, especially in the first 2 months after transplantation. During this period, TM subset levels sharply increased at acute rejection crisis and returned to previous values with rejection reversal. Our results suggest that the TM subset plays a prominent role in the mechanisms involved in the immunological response to allografts, and therefore repeated TM cell monitoring could be useful in the follow-up of renal transplant patients.

Pseudolymphoma of the lung: lymphoid subsets in the lung mass and in peripheral blood

Studies of the lymphocyte markers in a case of pseudolymphoma of the lung indicate a non-neoplastic nature of the lymphoid infiltrate. The relative proportions of T and B cells and of the markers for the various subsets of both populations reflect the morphologically mixed character of the cellular infiltrate of the lung mass. Moreover, an imbalance of T cell subsets was observed in the peripheral blood: the numbers of T cells with receptors for IgM (TM) were persistently decreased while an increase of the values of T lymphocytes with receptors for IgG (TG) was noted. In addition an altered immunologic status of the patient was indicated by the in vivo impairment of cellular immunity as demonstrated by the failure to respond to common antigens and to become sensitized to 1-chloro-2,4-dinitrobenzene (DNBC).

Human thymoma: immunologic characteristics of the lymphocytic component

Several immunologic parameters were investigated in the lymphocytic component of ten thymomas, characterized by a variable degree of lymphocytic infiltration. The majority of thymoma lymphocytes are T-cell in nature, as are lymphocytes from the normal thymus. Lymphocytes from six thymomas with moderate or predominant lymphocytic infiltrates were capable of forming stable E-rosettes, (mean percentage +/- SD: 78.0 +/- 5.2); binding peanut agglutinin (67.3 +/- 8.6); and exhibiting receptors for the Fc-portion of IgM (21.8 +/- 6.0) at percentages that were close to those found in the normal thymus. On the other hand, lower numbers of stable E-rosetting cells (26.8 +/- 8.7), PNA-positive cells (27.5 +/- 12.4), and remarkably higher percentages of cells with receptors for IgM (54.0 +/- 4.2) were demonstrated by the lymphocytic population of four thymomas with scant lymphocyte components. In addition, lymphocytes from tumors with scant lymphocyte components show a higher proliferative response to phytomitogen (PHA), therefore exhibiting immunologic features comparable to those of the more mature pool of normal medullary thymocytes. The observed immunologic similarities between the populations of lymphocytes from thymomas and from the normal thymus gland suggest an exclusively epithelial origin of the thymoma.

Distribution of IgG and IgM receptors on human peripheral natural killer cells measured on the level of the single effector cell

Using an agarose single-cell cytotoxicity assay simultaneously with the antibody-coated ox erythrocyte assay for detecting Fc receptor (FcR)-positive cells, the number of natural killer (NK) cells in fresh human peripheral blood which bear FcR for IgG or IgM have been determined. Of the target binding blood which bear FcR for IgG or IgM have been determined. Of the target binding cells (TBC) which form conjugates with NK-sensitive target cell lines Molt 4, 1301 and Hd-Mar, 55% had FcR for IgG and 24% had FcR for IgM. In the active NK cell population, which amounts to about 6% in nylon wool column-passed peripheral lymphocytes, cells with FcR for IgG account for 60% and cells with FcR for IgM for 17% of the total killing. Even though there is an increase in the number of FcR-IgM-positive cells from fresh peripheral blood after overnight incubation at 37 degrees C, no increase was found in FcR-IgM-positive NK cells. The reasons why FcR for IgM have not been described earlier on human NK cells are discussed, as well as the functional implications of these and their probable expression on other types of cytotoxic effector cells.

Lymphocyte subpopulations in non-neoplastic thymus from myasthenia gravis patients

Lymphocyte populations in non-neoplastic thymuses from fifteen patients with myasthenia gravis (MG) were examined. As in normal subjects, the great majority of thymic lymphocytes of MG patients are T cells. When MG thymuses were compared to normal glands, lower percentages of lymphocytes able to form E rosettes resistant to incubation at 37 degrees C (stable E rosettes) were found in MG thymuses. A negligible B cell content was detected in eight normal and in eight MG thymuses with absent or rare lymph follicles; but there was a substantial B cell presence in the thymuses of seven MG cases with thymic hyperplasia containing many germinal centres. Normal and MG thymuses contain the same percentage of lymphocytes bearing receptors for the Fc portion of IgM (TM). Moreover, the IgM Fc receptor was found mostly on cells which did not form stable E rosettes and did not bear surface immunoglobulin. The possible significance of these findings is discussed.