Membrane-bound immunoglobulins, receptors for the Fc fragment of IgG and receptors for the third component of human or murine complement were used as B cell membrane markers to study peripheral blood lymphocytes from twenty-two patients with chronic lymphatic leukemia (CLL), five patients with acute lymphoblastic leukemia (ALL) and one patient with Sézary syndrome. The capacity of human T cells of forming "spontaneous rosettes" with sheep erythrocytes was employed as T cell membrane marker. In nineteen out of twenty-seven CLL or ALL cases tested a larger percentage of cells than that found in normal individuals expressed at least one of the three B cell membrane markers studied. In the patient with Sézary syndrome the percentage of cells forming "spontaneous rosettes" with sheep erythrocytes was larger than the normal, while cells bearing B cells markers were below the normal values.
A serological cross-reactivity between env gp120 glycoprotein of the human immunodeficiency virus (HIV) and a human cellular surface protein has been defined by a monoclonal antibody (M38) raised against HIV. The cellular antigen is a protein of ca. 80 kDa expressed on a small fraction of mononuclear cells in peripheral blood and in lymph nodes. The protein behaves as an activation antigen of the monocytic lineage since it is expressed by monocytes in plastic-adherent culture conditions and by interferon-gamma-treated monocytes and pro-monocytic U937 cells. The protein is involved in antigen presentation since the antibody efficiently inhibits the proliferation of responsive lymphocytes in autologous tetanus toxoid presentation assays. In the T lymphoblastoid line H9, the protein is present in very small amounts, is not induced by interferon-gamma and increases after HIV infection. Sera from lymphoadenopathy syndrome and acquired immunodeficiency syndrome (AIDS) patients fail to detect the cellular protein, although containing antibodies reacting with gp120. We propose that both viral and cellular structures recognized by the monoclonal antibody (mAb) are involved in interactions with CD4 molecules of T helper lymphocytes and that such molecular mimicry might be relevant in the pathology of HIV infection. This view is supported by the finding that BL/10T4, a CD4-specific mAb, binds to M38 neutralizing its interactions with HIV and with monocytes. mAb M38 thus behaves as the internal image of CD4. This single property would explain all its diverse binding characteristics.
The turnover of IgM and IgD molecules present on the membrane of human tonsil cells has been studied using immunofluorescence and peroxidase-catalyzed membrane radioiodination. With the first of the two techniques cells were treated with pronase to remove membrane immunoglobulin (mIg), placed in culture and stained at intervals to check the reappearance of membrane IgD and IgM on the cell membrane. These experiments showed that membrane IgD (in contrast to membrane IgM) are extremely susceptible to proteolysis. Furthermore, cells treated with a concentration of pronase found to be optimal to remove membrane IgM failed to re-express membrane IgD in vitro. The large majority of tonsil lymphocytes has both membrane IgM and IgD. Due to the different behavior of reappearance of the two membrane molecules after treatment with pronase, it was not possible to obtain the simultaneous re-expression of membrane IgM and IgD by the cells "stripped" with pronase. However, the two molecules were re-expressed in vitro by the cells treated with different pronase concentrations with a similar timing, i.e. 50% or more of the cells re-expressed membrane IgD and IgM after 8 h in culture. 131I-radioiodinated membrane IgD and IgM were also released from the cell surface with a similar timing, the half-life of permanence on the cell membrane being about 4 h for both molecules. These findings thus indicate that IgM and IgD molecules have a similar turnover and that a cell is capable of placing two different Ig molecules at a time on its surface.
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