No abstract

The primary goal of this study was to determine how chronic exposure to Ag influences the functionality of Mycobacterium tuberculosis-specific T cell responses. The frequency of IFN-γ-producing effector CD4+ and CD8+ T cells dynamically changed during persistent M. tuberculosis infection. CD8+ T cells used differential effector functions during acute and chronic phases of the immune response, where CD8+ T cells produced negligible amounts of IFN-γ early in infection, but switched to cytokine production during the chronic stage of infection. Using limiting dilution analysis, CD8+ T cells isolated during the initial phase of infection demonstrated lytic potential, but this waned in the chronic stage. The apparent loss of cytotoxic activity was not associated with the lack of perforin. Ag dose could potentially govern the functional program of CD8+ T cells. Collectively, these results depict a host immune response mounted against M. tuberculosis of a significantly more dynamic nature than previously recognized.

Mycobacterium tuberculosis (Mtb) resides in a long-lived phagosomal compartment that resists maturation. The manner by which Mtb antigens are processed and presented on MHC Class I molecules is poorly understood. Using human dendritic cells and IFN-γ release by CD8+ T cell clones, we examined the processing and presentation pathway for two Mtb–derived antigens, each presented by a distinct HLA-I allele (HLA-Ia versus HLA-Ib). Presentation of both antigens is blocked by the retrotranslocation inhibitor exotoxin A. Inhibitor studies demonstrate that, after reaching the cytosol, both antigens require proteasomal degradation and TAP transport, but differ in the requirement for ER–golgi egress and new protein synthesis. Specifically, presentation by HLA-B8 but not HLA-E requires newly synthesized HLA-I and transport through the ER–golgi. Phenotypic analysis of the Mtb phagosome by flow organellometry revealed the presence of Class I and loading accessory molecules, including TAP and PDI. Furthermore, loaded HLA-I:peptide complexes are present within the Mtb phagosome, with a pronounced bias towards HLA-E:peptide complexes. In addition, protein analysis also reveals that HLA-E is enriched within the Mtb phagosome compared to HLA-A2. Together, these data suggest that the phagosome, through acquisition of ER–localized machinery and as a site of HLA-I loading, plays a vital role in the presentation of Mtb–derived antigens, similar to that described for presentation of latex bead-associated antigens. This is, to our knowledge, the first description of this presentation pathway for an intracellular pathogen. Moreover, these data suggest that HLA-E may play a unique role in the presentation of phagosomal antigens.

The adolescent period heralds the pediatric patient's transition into adulthood. It is a time of dynamic development during which effective preventive care measures can promote safe behaviors and the development of lifelong health habits. One of the foundations of preventive adolescent health care is timely vaccination, and every visit can be viewed as an opportunity to update and complete an adolescent's immunizations.In the past decade, the adolescent immunization schedule has expanded to include 2 doses of quadrivalent meningococcal conjugate vaccine, 1 dose of tetanus, diphtheria, acellular pertussis, absorbed vaccine, 2 or 3 doses of human papillomavirus vaccine, depending on the child's age, and an annual infl uenza vaccine. In addition, during adolescent visits, health care providers can determine whether catch-up vaccination is needed to meet early childhood recommendations for hepatitis B; hepatitis A; measles, mumps, rubella; poliovirus; and varicella vaccines. New serogroup B meningococcal vaccines are now available for those at increased risk for meningococcal disease; in addition, these serogroup B meningococcal vaccines received a Category B recommendation for healthy adolescents, where individual counseling and risk-benefi t evaluation based on health care provider judgements and patient preferences are indicated. This clinical report focuses on the epidemiology of adolescent vaccine-preventable diseases by reviewing the rationale for the annual universally recommended adolescent immunization schedule of the

Major histocompatibility complex (MHC) class I–restricted CD8+ T cells play a critical role in the protective immunity against Mycobacterium tuberculosis (Mtb). However, only a few Mtb peptides recognized by MHC class Ia–restricted CD8+ T cells have been identified. Information on epitopes recognized by class Ib–restricted T cells is even more limited. M3 is an MHC class Ib molecule that preferentially presents N-formylated peptides to CD8+ T cells. Because bacteria initiate protein synthesis with N-formyl methionine, the unique binding specificity of M3 makes it especially suitable for presenting these particular bacterial epitopes. We have scanned the full sequence of the Mtb genome for NH2-terminal peptides that share features with other M3-binding peptides. Synthetic peptides corresponding to these sequences were tested for their ability to bind to M3 in an immunofluorescence-based peptide-binding assay. Four of the N-formylated Mtb peptides were able to elicit cytotoxic T lymphocytes (CTLs) from mice immunized with peptide-coated splenocytes. The Mtb peptide–specific, M3-restricted CTLs lysed the Mtb-infected macrophages effectively, suggesting that these N-formylated Mtb peptides are presented as the naturally processed epitopes by Mtb-infected cells. Furthermore, T cells from Mtb-infected lungs, spleen, and lymph nodes responded to N-formylated Mtb peptides in an M3-restricted manner. Taken together, our data suggest that M3-restricted T cells may participate in the immune response to Mtb.