Differential activation of CD4+ T-cell precursors in vivo leads to the development of effectors with unique patterns of lymphokine secretion. To investigate whether the differential pattern of lymphokine secretion is influenced by factors associated with either the display and/or recognition of the ligand, we have used a set of ligands with various class II binding affinities but unchanged T-cell specificity. The ligand that exhibited -10,000-fold higher binding to I-AU considerably increased the frequency of interferon y-producing but not interleukin (IL) 4-or IL-5-secreting cells in vivo. Using an established ligand-specific, CD4+ T-cell clone secreting only IL-4, we also demonstrated that stimulation with the highest affinity ligand resulted in interferon 'y production in vitro. In contrast, ligands that demonstrated relatively lower class II binding induced only IL-4 secretion. These data suggest that the major histocompatibility complex binding affinity of antigenic determinants, leading to differential interactions at the T cell-antigenpresenting cell interface, can be crucial for the differential development of cytokine patterns in T cells.

Acute promyelocytic leukemia (APL) is a highly aggressive disease requiring prompt diagnosis and specific early intervention. Immunophenotyping by flow cytometry (FCM) facilitates a rapid diagnosis, but commonly used criteria are neither sufficiently sensitive nor specific. With an antibody panel for diagnostic screening in routine practice, we found all 149 APL cases in this study exhibited a unique immunophenotypic profile, ie, a characteristic CD11b- myeloid population and absent CD11c expression in all myeloid populations; 96.6% of cases also lacked HLA-DR expression. These distinctive features allowed recognition of all unusual cases phenotypically resembling the regular myeloblasts (CD34+/HLA-DR+) or granulocytes (CD117-/CD34-/HLA-DR-). FCM effectively identified all 19 APL cases with variant translocations, including cases with a normal karyotype due to a cryptic submicroscopic t(15;17)(q22;q21), t(11;17)(q23;q21) that escaped the detection by fluorescence in situ hybridization for t(15;17) and der(15)ider(17)(q10) that lacked a simple reciprocal t(15;17). When APL-associated profiles were validated against 107 AML cases of non-APL subtypes, including 51 HLA-DR- cases, the diagnostic specificity and positive predictive value were 98%. FCM effectively provides independent detection of APL during diagnostic workup and harmonizes with the subsequent molecular cytogenetic diagnosis.

The mechanism of immunodominance was investigated using chimeric peptides from mouse myelin basic protein consisting of the immunodominant I-Au-restricted Ac1-11, attached by a peptide bond to I-Eu-restricted 35-47. Our results indicate that this chimeric peptide and certain of its derivatives were excellent immunogens both in vitro and in vivo. Notably, on immunization with Ac1-11:35-47 or Ac1-11 (Ala4):35-47, the proliferative T cell responses to each of its component peptides were almost completely "subjugated" in favor of neo-determinants that are I-Eu restricted. Furthermore, each of 11 hybridomas derived after immunization with Ac1-11:35-47 had specificity for junctional neo-determinants and none could be stimulated to produce interleukin-2 from Ac1-11 or 35-47. Subjugation of the immunogenicity of the original determinants occurred regardless of their dominance when separate. It did not appear to result from non-availability of the original determinants because the chimeric peptide was able to induce neonatal tolerance to each of its constituents. These results indicate that in an overlapping multideterminant array, the dominant determinant is unpredictable from historical data about any of the components. Determinant choice, at any stage of processing, may be governed by competitive aspects of determinant capture in an environment where all components--antigen, major histocompatibility complex and T cell receptor--are available.

The processing and presentation of whole irradiated Mycobacterium tuberculosis (Mtb gamma) and its purified protein derivative (PPD) by the peripheral blood monocytes from healthy Bacillus Calmette Guérin (BCG)-vaccinated individuals was investigated. To study processing and presentation as events distinct from T cell recognition and proliferation, monocytes were pulsed with antigens for varying time intervals and fixed. The kinetics of presentation indicate that up to 2 h was required for effective presentation of PPD and 2-4 h for Mtb gamma, and that the ability to activate T cells declined as the time interval for which pulsing occurred was increased, so that responses were abolished by 8-10 h. Prefixed monocytes could not present Mtb gamma and PPD to T cells indicating that processing was an essential requisite. Lysosomotropic agents chloroquine, monensin, and leupeptin inhibited the presentation of these antigens suggesting the role of lysosomes/endosomes in processing. Furthermore, monocytes incubated with optimal concentration of antigens for different lengths of time released determinants which were still antigenic but circumvented the need for any further processing. Addition of nonprimed syngeneic monocytes, both untreated or paraformaldehyde fixed to cells which had been pulsed and fixed, restored the responses even at the later time periods when responses were not detected. This second interaction of the monocyte with T cells was not major histocompatibility complex restricted in that the addition of monocytes from another donor was equally effective.

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