Posts Tagged ‘cell-mediated immunity’

New Coronavirus Passive Vaccine Developed by Israeli Researchers

Reporter: Irina Robu, PhD

Researchers at Bar-Ilan University have identified short amino acid sequences that could help the development of a vaccine against COVID-19 virus. Of the 25 epitopes that were discovered to be 100% identical to SARS, seven are theoretically efficient vaccine candidates. Their research indicate that they could cover as much as 87% of the world population

Their study has identified a set of immunodominant epitopes from the SARS-CoV-2 proteome, which are capable of generating antibody and cell mediated immune responses. The epitopes, known as antigenic determinants, are the part of the antigen that binds to a specific antigen receptor on the surface of B cells or T cells and are able to provoke an immune response.

It is known that immune response occurs within an organism for the purpose of defending against foreign invaders such as viruses, bacteria, parasites and fungi. The immune responses that are based on specific immunodominant epitopes contain the generation of both antibody- and cell-mediated immunity against pathogens. Such immunity can facilitate fast and effective elimination of the pathogen. The end result is a passive vaccine capable of capable of activating both cellular and humoral immune responses in humans.

According to the team at Bar-Ilan University, the mapped coronavirus epitopes with those of the influenza virus. And they found that 85% of the sequence identity with experimentally detected epitopes of Severe Acute Respiratory Syndrome-related coronavirus (SARS-CoV).

Additional analysis indicated that the epitopes are non-allergic and non-toxic to humans and have very low risk for generating autoimmune responses. The team is looking to partner with companies to build vaccine constructs and test them in-vitro and on animal trials before starting any clinical trials.



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Signaling through the T Cell Receptor (TCR) Complex and the Co-stimulatory Receptor CD28

Curator: Larry H. Bernstein, MD, FCAP



New connections: T cell actin dynamics

Fluorescence microscopy is one of the most important tools in cell biology research because it provides spatial and temporal information to investigate regulatory systems inside cells. This technique can generate data in the form of signal intensities at thousands of positions resolved inside individual live cells. However, given extensive cell-to-cell variation, these data cannot be readily assembled into three- or four-dimensional maps of protein concentration that can be compared across different cells and conditions. We have developed a method to enable comparison of imaging data from many cells and applied it to investigate actin dynamics in T cell activation. Antigen recognition in T cells by the T cell receptor (TCR) is amplified by engagement of the costimulatory receptor CD28. We imaged actin and eight core actin regulators to generate over a thousand movies of T cells under conditions in which CD28 was either engaged or blocked in the context of a strong TCR signal. Our computational analysis showed that the primary effect of costimulation blockade was to decrease recruitment of the activator of actin nucleation WAVE2 (Wiskott-Aldrich syndrome protein family verprolin-homologous protein 2) and the actin-severing protein cofilin to F-actin. Reconstitution of WAVE2 and cofilin activity restored the defect in actin signaling dynamics caused by costimulation blockade. Thus, we have developed and validated an approach to quantify protein distributions in time and space for the analysis of complex regulatory systems.



Triple-Color FRET Analysis Reveals Conformational Changes in the WIP-WASp Actin-Regulating Complex



T cell activation by antigens involves the formation of a complex, highly dynamic, yet organized signaling complex at the site of the T cell receptors (TCRs). Srikanth et al. found that the lymphocyte-specific large guanosine triphosphatase of the Rab family CRACR2A-a associated with vesicles near the Golgi in unstimulated mouse and human CD4+ T cells. Upon TCR activation, these vesicles moved to the immunological synapse (the contact region between a T cell and an antigen-presenting cell). The guanine nucleotide exchange factor Vav1 at the TCR complex recruited CRACR2A-a to the complex. Without CRACR2A-a, T cell activation was compromised because of defective calcium and kinase signaling.

More than 60 members of the Rab family of guanosine triphosphatases (GTPases) exist in the human genome. Rab GTPases are small proteins that are primarily involved in the formation, trafficking, and fusion of vesicles. We showed that CRACR2A (Ca2+ release–activated Ca2+ channel regulator 2A) encodes a lymphocyte-specific large Rab GTPase that contains multiple functional domains, including EF-hand motifs, a proline-rich domain (PRD), and a Rab GTPase domain with an unconventional prenylation site. Through experiments involving gene silencing in cells and knockout mice, we demonstrated a role for CRACR2A in the activation of the Ca2+ and c-Jun N-terminal kinase signaling pathways in response to T cell receptor (TCR) stimulation. Vesicles containing this Rab GTPase translocated from near the Golgi to the immunological synapse formed between a T cell and a cognate antigen-presenting cell to activate these signaling pathways. The interaction between the PRD of CRACR2A and the guanidine nucleotide exchange factor Vav1 was required for the accumulation of these vesicles at the immunological synapse. Furthermore, we demonstrated that GTP binding and prenylation of CRACR2A were associated with its localization near the Golgi and its stability. Our findings reveal a previously uncharacterized function of a large Rab GTPase and vesicles near the Golgi in TCR signaling. Other GTPases with similar domain architectures may have similar functions in T cells.


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