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L Lefrancois

Publications and source records attributed to L Lefrancois.

At least 37 records · Page 2Linked to original sources
PubMed1989

In vivo modulation of cytolytic activity and Thy-1 expression in TCR-gamma delta+ intraepithelial lymphocytes.

Although the functional aspects of the alpha beta T cell antigen receptor (TCR) found on most peripheral T cells are well described, the function of the gamma delta TCR remains unclear. Murine intraepithelial lymphocytes (IEL) of the small intestine are CD8+, express the gamma delta TCR, and are constitutively lytic. Fresh IEL from germ-free mice had no lytic activity. Moreover, whereas IEL from normal mice are 30 to 50 percent Thy-1+, IEL from germ-free did not express Thy-1. Acclimation of germ-free mice to nonsterile conditions resulted in the generation of Thy-1+ IEL and induction of lytic activity. Thus CD8+ TCR-gamma delta IEL were regulated by externally derived stimuli via a specific functional interaction between IEL and gut-associated antigens.

Animals↗
PubMed1988

Monoclonal antibodies specific for T cell-associated carbohydrate determinants react with human blood group antigens CAD and SDA.

The CT antigenic determinants have previously been shown to be present on the T200 glycoproteins and other proteins of murine cytotoxic T cell clones but not of T helper clones or nonactivated lymphocytes (1, 2). Two determinants recognized by mAbs CT1 and CT2 are also expressed on thymocytes in a developmentally regulated fashion during fetal thymus ontogeny and are found in a subset of Lyt-2+ intraepithelial lymphocytes in the intestinal mucosa (3-5). Previous studies of the biosynthesis of CT+ proteins suggested that these determinants were composed of carbohydrate (8). We now demonstrate that the anti-CT mAbs react with a carbohydrate determinant at the nonreducing terminus of O-linked oligosaccharides that has the configuration GalNAc beta 1,4[SA alpha 2,3]-galactose. The CT antibodies detected this determinant not only on CTL clones but also in the human blood group antigens Cad and Sda+. Variant CTL lines, non-Cad erythrocytes, and Sda- glycoproteins that lacked the GalNAc residue did not bind the CT mAb. Sialic acid was essential for CT antigen expression since neuraminidase or mild periodate treatment abrogated CT antibody binding. In addition, other carbohydrate structures with terminal GalNAc residues such as the A or Tn blood group antigens were not recognized. The CT antibodies thus define GalNAc and sialic acid containing carbohydrate antigens that are expressed on discrete subsets of T lymphocytes and may also be useful reagents for the detection of Cad and Sda+ blood group antigens.

Animals↗
PubMed1987

Developmental sequence of T200 antigen modifications in murine T cells.

The T200 glycoproteins of T cells were analyzed at different stages of T cell development. Immunoprecipitation and analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that Lyt-2-L3T4-, and Lyt-2+L3T4+ thymocytes had similar T200 proteins, whereas Lyt-2+L3T4- and Lyt-2-L3T4+ thymocytes expressed a distinct set of T200 molecules. This result indicated a molecular switch in regulation of T200 protein expression upon differentiation of thymocytes to mature phenotype T cells. Further modifications were evident when the T200 proteins of peripheral T cell subsets were examined. In particular L3T4+ T cells expressed T200 proteins of m.w. 220,000, 200,000, and 175,000, whereas Lyt-2+ lymph node T cells expressed an additional T200 protein of m.w. 235,000. Antigenic differences in the T200 glyco-proteins of peripheral L3T4+ and Lyt-2+ T cells were also detected. The anti-B220 monoclonal antibody, 14.8, reacted with lymph node Lyt-2+ T cells but did not react with lymph node L3T4+T cells or with Lyt-2+L3T4- thymocytes. This finding demonstrated a lineage-specific modification of the T200 protein of Lyt-2+ T cells that occurred after exit of these cells from the thymus into peripheral lymphoid organs. This modification apparently occurred on the m.w. 235,000 and 220,000 proteins since these species were precipitated by 14.8, whereas the others were not. In vitro growth and activation also resulted in further T200 antigen alterations. The monoclonal antibody, RA3, which reacts with the B220 antigen of B cells but, unlike 14.8, does not react with any peripheral T cells, showed significant reactivity with Lyt-2+ cytotoxic T cell (CTL) clones but not with L3T4+ T helper cell clones. CTL clones were also 14.8+ but T helper cell clones were not. Immunoprecipitation by 14.8 and RA3 of T200 proteins from CTL clones yielded a single protein of m.w. 240,000 that co-migrated with the B cell form of T200. Overall, the results indicate the presence of developmentally regulated mechanisms that control T200 glycoprotein expression during T cell differentiation in the thymus and in peripheral lymphoid organs.

Animals↗
PubMed1987

Expression of carbohydrate differentiation antigens during ontogeny of the murine thymus.

Two monoclonal antibodies, CT1 and CT2, have recently been described that recognize cell type restricted carbohydrate determinants present on the T200 glycoprotein of murine cytotoxic T lymphocytes in vitro. I have now examined the expression of the CT antigens in the developing thymus by using immunohistology to discern in situ expression, and cytofluorographic analysis of isolated fetal thymocyte populations to analyze cell subset distribution of the CT antigens. Immunohistology demonstrated that the pattern of CT antigen expression progressed developmentally with a relatively homogeneous distribution throughout the thymus during early thymus ontogeny and a distinct subcapsular pattern late in gestation. Fluorescence flow cytometry analyses showed that at all times the CT1 antigen was expressed exclusively by a subset of the Lyt-2- L3T4-, interleukin 2 receptor+ blast cell population. In contrast, the CT2 antigen was expressed on a subpopulation of small Lyt-2+ L3T4+ thymocytes as well as on some Lyt-2- L3T4- cells. Radioimmunoprecipitation indicated that the CT1 antigen was present on the T200 glycoprotein. Although forms of the T200 glycoprotein are found on cells of all hematopoietic lineages except those of erythroid descent, the CT determinants are found only on a restricted subset of T200-expressing lymphocytes. These findings suggest a fundamental role for carbohydrate moieties and for the T200 molecule in T cell development.

Acetylgalactosamine↗
PubMed1987

Characterization of dual-reactive H-2Kb-restricted anti-vesicular stomatitus virus and alloreactive cytotoxic T cells.

Cross-reactive recognition of alloantigen by "self + X"-reactive cytotoxic T lymphocytes (CTL) has been documented in a variety of systems. It has been shown previously that the H-2Kb-restricted CTL response of C57BL/6 (B6) mice to vesicular stomatitis virus (VSV) infection is partially cross-reactive on uninfected target cells expressing the H-2Kbm8 mutation. In this report, we describe the isolation and detailed characterization of such dual-reactive CTL. By employing EL4 tumor lines transfected with genes encoding various VSV proteins, we demonstrated that the majority of dual-reactive CTL recognize the internal N protein of VSV and are also reactive against uninfected bm8 targets. Although the response of normal B6 mice to bm8 stimulators shows no measurable cross-reactivity on VSV-infected targets, the response of VSV-primed B6 mice to bm8 stimulation is almost entirely cross-reactive, lysing VSV-B6 targets and uninfected bm8 targets roughly equally. Furthermore, about 70% of CTL clones isolated from such mice by bm8 stimulation are dual-reactive with respect to effector function. Analysis at the population and clonal levels with cold target competition and antibody blocking suggests that the bulk of dual-reactive CTL have a higher avidity for VSV-B6 targets than for bm8 targets. The extreme case of this is illustrated by a fraction of CTL clones, isolated and maintained on bm8 stimulators, which lyse VSV-B6 targets but do not lyse bm8 targets. One such CTL clone is shown to be specific for the bm8 antigen in proliferation assays. These results demonstrate that: the specificity of an alloreactive CTL response may be dramatically altered by previous antigenic encounters; and dual-reactive CTL display a significant difference in affinity of the CTL receptor-determinant interaction, depending on the target which is recognized.

Animals↗
PubMed1987

Carbohydrate differentiation antigens of murine T cells: expression on intestinal lymphocytes and intestinal epithelium.

Carbohydrate differentiation antigens (CT antigens) which previously had been shown to be associated with cytotoxic T cells were found at high levels on intestinal intraepithelial lymphocytes (IEL) and on the intestinal epithelium. Histological examination of intestinal sections demonstrated that the CT1 MAb defined epitopes on IEL and on epithelial cells located in the base of the villi crypts. The CT2 MAb reacted with IEL but also bound to the majority of cells in the intestinal epithelium. When isolated intestinal cell populations were analyzed by flow cytometry, two major size classes of cells were evident. The smaller cells, corresponding to lymphocytes, were primarily Lyt-2+, with a high proportion expressing CT antigens. Another differentiation antigen defined by the MAb J11d was absent from IEL, indicating that those IEL of T cell origin are likely to be mature because thymocytes, but not peripheral T cells, express the J11d antigen. Two-color fluorescence analysis indicated that the CT determinants were present on the Thy-1+, Lyt-2+, and the Thy-1-, Lyt-2+ subsets of IEL. However, the small percentage of L3T4+ IEL were CT-, further supporting our previous demonstration of a correlation between CT expression and Lyt-2 expression. Interesting phenotypic characteristics of IEL other than CT antigen expression were also detected. IEL did not express the MEL-14 lymphocyte homing receptor, and the cell surface level of LFA-1 was significantly lower than that of other peripheral lymphocytes. It was also shown that a small percentage of IEL express a T cell receptor allotypic marker, indicating that at least some of the cells are mature in terms of T cell receptor gene rearrangements. The large intestinal cells, although CT+, were not hematopoietic in origin because they were T200- and were shown by using chimeric mice not to be bone marrow-derived. In contrast to previously reported results, the cytotoxic activity of IEL was negligible with detectable lysis against NK-sensitive cells and other tumor cells, being observed in only one of seven experiments. Thus, the expression of the CT determinants was not indicative of cytotoxic ability, as previously suggested. The presence of specific carbohydrate residues on the cell surface of a subset of lymphocytes in an anatomically distinct immune compartment suggests that a unique differentiation pathway is followed by these cells.

Animals↗
PubMed1986

Recognition of cloned vesicular stomatitis virus internal and external gene products by cytotoxic T lymphocytes.

It has generally been assumed that most if not all CTL specific for vesicular stomatitis virus (VSV)-infected cells recognize the viral glycoprotein (G), an integral membrane protein abundantly expressed on infected cell surfaces. Using recombinant vaccinia viruses containing copies of cloned VSV genes to examine CTL recognition of VSV, we have confirmed that G is recognized by VSV-specific CTL. More interestingly, however, we have also found that nucleocapsid protein (N), an internal virion protein, can be detected on infected cell surfaces using mAb, and serves as a major target antigen for VSV-specific CTL. In contrast to the highly serotype-specific recognition of G, N is recognized by a major population of CTL able to lyse cells infected with either the Indiana or New Jersey VSV serotypes. Using target cells expressing a cloned MHC class I gene, we could directly show that CTL recognition of N occurs in the context of the MHC Ld molecule.

Animals↗
PubMed1986

Different classes of T lymphocytes have different mRNAs for the leukocyte-common antigen, T200.

The leukocyte common antigen, T200, is expressed on all white blood cells but not on other differentiated cells. Within the hematopoietic lineage, specific cell types display characteristic structural forms of the molecule on their surface. We show that murine cytotoxic T lymphocyte clones and helper T cell clones contain different size mRNA for this molecule, and that the early precursors of T200 glycoprotein made in the helper and cytotoxic T cells differ in Mr. Thus, in addition to differences in posttranslational modifications, it is highly likely that a difference in protein structure contributes to the distinct forms of T200 glycoprotein found on these functional T cell subsets.

Animals↗
PubMed1986

Coordinate expression of cytolytic activity and cytotoxic T cell-specific carbohydrate antigens in a T cell hybridoma.

The expression of cytotoxic T lymphocyte (CTL)-specific carbohydrate antigens (termed CT antigens) was studied by using a cytolytically inducible T cell hybridoma, KSH4.13.6. Expression of the CT determinants occurred concomitantly with the expression of cytolytic activity after induction of the hybrid with supernatants from Con A-activated rat spleen cells. Purified IL 2 was also proven to be effective in inducing cytolytic activity and CT antigen expression, but the time course of activation by IL 2 was prolonged as compared to activation by crude supernatants. Furthermore, the activation process was reversible because removal of the hybrid from inducing medium resulted in the loss of cytolytic capability and CT antigen expression. By separating the low and high expressors of CT antigen from an induced hybrid population, it was shown that the level of CT antigen expression correlated with the cytolytic ability of the hybrid. High expressors of CT antigen exhibited four- to 50-fold greater lytic activity than populations with low CT antigen levels. Binding experiments using lectins indicated that an increase in GalNAc-containing oligosaccharides also occurred on activation of the hybrid. This finding agrees with our results which indicated that the CT carbohydrate antigens are probably associated with O-linked glycans. Because our previous results with CTL clones indicated that the CT antigens were associated with the T200 glycoproteins, we performed immunoprecipitation experiments with surface-labeled induced and uninduced KSH4.13.6. The T200 glycoproteins were precipitated by the CT1 monoclonal antibody from the induced population, but not from the uninduced population. Furthermore, precipitation by the GalNAc-recognizing lectin from Vicia villosa revealed marked differences in the GalNAc-containing proteins between the induced and uninduced populations. Thus, the results indicate that the T cell-derived polypeptide hormone IL 2 is able to influence the glycosylation of specific proteins in CTL, which results in the appearance of carbohydrate antigens whose expression is linked to the activation state of the CTL.

Animals↗
PubMed1986

Sequences of the major antibody binding epitopes of the Indiana serotype of vesicular stomatitis virus.

A panel of neutralizing and nonneutralizing monoclonal antibodies (MAbs) to the Indiana strain of vesicular stomatitis virus (VSV-IND) were used to select nonbinding VSV-IND mutants. In addition, virus was passaged against high titered polyclonal antisera to select for poorly neutralized virus mutants. Nucleic acid sequencing localized mutations in the surface spike glycoprotein (G protein) sequence which were associated with decreased neutralization by polyclonal antisera and with nonbinding by neutralizing and nonneutralizing MAbs. The major neutralization epitope, the A epitope, is composed of at least two regions that are widely separated in the primary G protein sequence. We found evidence for both continuous and discontinuous determinants within the A epitope and found one strongly selected region that may function as an antigenic loop. The high degree of sequence homology between VSV-IND and the other major VSV serotype, VSV-New Jersey (VSV-NJ) allowed us to predict some of the neutralization epitopes of VSV-New Jersey. Alignment of VSV and rabies virus sequences revealed that major neutralizing epitopes in VSV correspond to sites of carbohydrate attachment in rabies. This may be of significance in the evolution of rhabdoviruses.

Amino Acid Sequence↗
PubMed1985

Acquisition of cytotoxic T lymphocyte-specific carbohydrate differentiation antigens.

Cytotoxic T cell (CTL)-specific activation antigens, termed CT determinants, have been detected by monoclonal antibodies (mAb) that inhibit CTL function. At the cell surface, the CT antigens are associated with the T200 glycoproteins and two other proteins of Mr 140,000 and 85,000 and are present on a secreted protein, gp155. Periodate treatment followed by binding analysis and immunoprecipitation experiments using tunicamycin-treated cells indicated that carbohydrate is necessary for CT antigen expression. Furthermore, gp155 is secreted in the presence of tunicamycin while retaining the CT antigens, and the CT determinants are added late in T200 biosynthesis, suggesting that the CT glycans are O-linked. Finally, interleukin 2 was shown to dramatically influence the expression of the CT mAb-reactive oligosaccharides present at the CTL cell surface.

Animals↗
PubMed1985

A murine cytotoxic T lymphocyte clone from the intestinal mucosa that is antigen specific for proliferation and displays broadly reactive inducible cytotoxic activity.

Thy-1+, Lyt-1-,2+, asialo GM1+ cytotoxic T lymphocyte (CTL) clones have been isolated from the intestinal mucosa of mice primed with alloantigens. Two different types of cytotoxic clones have been obtained. The first type is functionally similar to most splenic and lymph node-derived CTL clones in that they are strictly antigen specific with respect to proliferation and cytolytic activity. The second type of CTL clone has several unique characteristics. Although these clones are also antigen specific with regard to proliferation, they are not cytolytic under standard growth conditions in medium containing 4% rat concanavalin A-induced spleen cell supernatant. After culture for 4 days in the presence of high concentrations of interleukin 2, cells become activated and exhibit broad lytic potential. Moreover, during the activation process, these CTL begin to express a murine T cell surface antigen, CT-1, which is associated with activated cytotoxic cells. The findings reported in this report should now allow us to precisely define, both phenotypically and functionally, specific lymphocyte populations that make up the gut-associated lymphoid tissues. These data also describe a new type of effector CTL that differs from other cytotoxic cells reported to date, because it is antigen dependent for proliferation, but requires signals mediated by lymphokines for lytic activation.

Animals↗
PubMed1984

Protection against lethal viral infection by neutralizing and nonneutralizing monoclonal antibodies: distinct mechanisms of action in vivo.

Monoclonal antibodies (MAb) reactive with the glycoprotein of vesicular stomatitis virus (VSV) serotypes Indiana (VSV-Ind) and New Jersey (VSV-NJ) were used to protect mice against lethal infection. MAb which reacted with a number of distinct epitopes and which could neutralize the virus in vitro could also protect against infection in vivo. MAb which could not neutralize the virus in vitro but which were specific for the glycoprotein of a single serotype were also able to protect mice against lethal VSV challenge. Interestingly, a group of MAb which cross-reacted with the glycoproteins of VSV-Ind and VSV-NJ could passively protect against challenge with either serotype. It was shown that as early as 2 h after infection, neither neutralizing nor nonneutralizing MAb could protect. Nonneutralizing MAb were found to be less effective at in vivo protection than neutralizing MAb. Furthermore, nonneutralizing MAb demonstrated a much lower binding efficiency to intact virions than did neutralizing MAb. These observations, plus the fact that the nonneutralizing MAb could lyse virus-infected cells in the presence of complement, suggested that in vivo protection by these antibodies may involve cell-associated viral determinants. To compare the mechanisms by which neutralizing and nonneutralizing MAb protected in vivo, F(ab')2 fragments were used in protection experiments. Although the F(ab')2 of a neutralizing MAb was still able to protect animals lethal virus challenge, the F(ab')2 of a cross-reactive nonneutralizing MAb was unable to do so. The reactivity of nonneutralizing MAb with virions and the apparent necessity of an intact Fc portion for protection further distinguish these antibodies from those MAb that are able to neutralize VSV solely by binding to the glycoprotein.

Animals↗
PubMed1984

Antigen-independent activation of memory cytotoxic T cells by interleukin 2.

Culture supernatants from mitogen- or antigen-activated murine spleen cells are capable of causing reexpression of specific cytolytic activity from inactive memory cytotoxic T lymphocytes (CTL) in the absence of the original priming antigen. We have demonstrated that memory CTL from cytolytically inactive day 14 MLC cells are induced to reexpress high levels of specific cytotoxic activity after incubation with IL 2. Highly purified IL 2 was shown to induce levels of lytic activity comparable with that induced by supernatants from secondary mixed lymphocyte cultures (secondary MLC SN), suggesting that only IL 2 is necessary for the reactivation process. Moreover, only Lyt-2+ cells are necessary for reactivation inasmuch as inactive MLC cells depleted of Lyt-1+ cells by treatment with antibody and complement, followed by FACS selection of Lyt-2+ cells, were efficiently reactivated by IL 2. Because IL 2 is considered a proliferative signal, we examined whether proliferation was requisite for reactivation of memory CTL by IL 2. In the presence of cytosine arabinoside, which effectively inhibited proliferation, IL 2 was capable of reactivating memory CTL as efficiently as antigen, thus implying a differentiative role for IL 2 in secondary CTL activation. Reactivation of CTL by IL 2 and antigen appear to be functionally distinct events, because antigen but not IL 2 could trigger immune interferon release, although either IL 2 or antigen induced high levels of cytotoxicity. We propose that resting, memory CTL retain a heightened level of expression of IL 2 receptors as compared with naive CTL precursors, and thus are able to respond directly to exogenous IL 2. The consequences of this are proliferation and reexpression of specific killing activity, but this signal is not sufficient to induce immune interferon secretion. Rather, it appears that a signal via the antigen receptor is necessary for release of this lymphokine.

Animals↗
PubMed1984

Studies on the mechanism of suppression of primary cytotoxic responses by cloned cytotoxic T lymphocytes.

We have shown in the accompanying companion paper that cloned cytotoxic T lymphocytes (CTL) can serve as veto cells in vitro, suppressing primary cytotoxic activity directed against antigens expressed by those cloned CTL but not against third party antigens. We now explore the mechanism of this antigen-specific suppression by cloned CTL, using as a model system the ability of G4, a BALB.B anti-H-2Dd CTL clone, to specifically suppress a primary in vitro anti-H-2b CTL response. G4 cells do not constitutively secrete a suppressor factor, because suppression cannot be mediated by supernatants removed from G4 cells at a time when they are routinely used as veto cells. Furthermore, medium removed from cultures suppressed by G4 will not suppress, indicating that the veto cell function of G4 is not mediated by soluble factors. Full suppression of primary anti-H-2b CTL responses requires that G4 be present throughout the 5-day mixed lymphocyte culture (MLC). Removal of G4 during the first 3 days of MLC results in a drastic reduction in the level of antigen-specific suppression, with a slight but reproducible loss of suppression after veto cell removal on day 4. The addition of G4 during the course of an ongoing MLC reveals that maximal suppression requires the presence of veto cells during the first 24 to 48 hr of culture. Thus, G4 cells must be present both early and late in an MLC to exert maximal veto cell suppression. Several experiments suggest that G4-induced veto cell activity is unlikely to be due to cytolysis of CTL precursors which are capable of recognizing G4. G4 cannot specifically recognize these CTL precursors, and G4 cells are inefficient at lectin-mediated lysis of non-tumor cell targets. Furthermore, we show that G4 cells cannot lyse CTL which recognize them. Finally, dilutions of anti-clonotypic antibodies which completely block both lectin-mediated and specific cytolysis by G4 do not block (and in fact enhance) G4-mediated veto cell activity.

Animals↗
PubMed1983

Antigenic determinants of vesicular stomatitis virus: analysis with antigenic variants.

Antigenic variants of vesicular stomatitis virus (VSV) serotypes New Jersey and Indiana (VSV-NJ, VSV-Ind) were selected by using a panel of monoclonal antibodies (MAb) specific for the major surface glycoprotein (G-protein). The reactivity of antigenic variants with the panel of MAb confirmed observations made by competitive binding assays that four distinct antigenic sites (A-D)NJ on the VSV-NJ G-protein and four partially overlapping sites (A, B1, B2, C)Ind on the VSV-Ind G-protein are involved in virus neutralization. Furthermore, subregions within the A epitopes of both serotypes were detected by variant analysis. The frequency of variation at most epitopes was 1 in 10(5) for VSV-NJ and 1 in 10(6) for VSV-Ind. The A3 and C determinants of VSV-Ind, however, defined by MAb that exhibited overlap in binding to other epitopes, appeared to be relatively invariant. Multiple mutations may be necessary to abolish antibody binding at these sites. Overlap of the C group of anti-VSV-Ind MAb with the A epitopes was assigned to the A2 subregion, because variants selected with A2 MAb show reduced binding of C MAb. Heterogeneous antisera from a primary immune response could detect differences in reactivity between variants at the A epitopes and wild-type VSV-NJ or VSV-Ind, suggesting the A epitope is immunodominant. Hyperimmune sera could detect a small difference between ANJ and BNJ variants compared to wild-type VSV-NJ, but could not distinguish between VSV-Ind variants and wild-type VSV-Ind.

Antibodies, Monoclonal↗
PubMed1983

Cytotoxic T lymphocytes reactive with vesicular stomatitis virus: analysis of specificity with monoclonal antibodies directed to the viral glycoprotein.

A panel of monoclonal antibodies (MAb) reactive with the vesicular stomatitis virus (VSV) glycoprotein (G-protein) was used to inhibit lysis of infected target cells by cytotoxic T lymphocytes (CTL) reactive with VSV serotypes Indiana and New Jersey (VSV-Ind, VSV-NJ). MAb to distinct epitopes on the VSV-NJ G-protein were able to block lysis of VSV-NJ-infected targets using anti-VSV-NJ CTL. Furthermore, when a combination of MAb to three distinct epitopes was used, increased inhibition was observed when compared to single epitope blocking. Cross-reactive CTL generated using either VSV-NJ or VSV-Ind could be inhibited by MAb specific for the heterologous virus in blocking assays. Cross-reactive MAb also were able to block both serotype-specific and cross-reactive lysis. Antigenic variants selected with some of the MAb used in blocking studies were used to infect target cells. Reduction in lysis was not observed using variants with mutations at several epitopes. This result suggests that blocking by MAb involves steric hindrance of CTL-recognized determinants proximal to the MAb binding site.

Animals↗