Expression of co-stimulatory molecules B7.1 & B7.2 on macrophages infected with various strains of Mycobacterium tuberculosis & its influence on T-cell apoptosis

Indian J Med Res. 2008 Apr;127(4):388-94.

Abstract

Background & objective: Activation of T cells is mediated through two critical signals provided by activated macrophages. The first signal is triggered when T cell receptor (TCR) binds to the major histocompatibility antigen (MHC/Ag) complex. The second signal is the interaction of co-stimulatory molecules with their respective ligands on T cells for their activation and proliferation. We undertook this study to observe the modulation in B7.1 (CD80) and B7.2 (CD86) co-stimulatory molecules on Mycobacterium tuberculosis infected monocyte derived macrophages (MDM) and their role in T helper (Th1) cell apoptosis.

Methods: M. tuberculosis clinical strains (S7 and S10) and laboratory strains (H37Ra and H37Rv) were used to infect the MDMs. The modulation of apoptosis was assessed by treating T cells with anti-CD3 and anti-CD28 antibodies. The infected MDMs were co-cultured with autologous PPD pulsed T cells to ascertain the role of co-stimulatory molecules during infection.

Results: In infected MDMs, all strains on day 1 but only S7 on day 2 showed significant decrease (P<0.05) in B7.1 expression compared to uninfected. The expression levels of B7.2 were also low on day 1 in S7, S10 and H37Ra infected MDMs. The anit-CD3 induced apoptosis in PPD pulsed Tcells showed further reduction with anti-CD28 antibodies. However, the modulation observed in B7.1 expression in infected MDMs was not reflected in T cell apoptosis in co-culture experiments.

Interpretation & conclusion: Our results confirmed the role of B7.1 in rescuing the activated Tcells from undergoing apoptosis. During infection when the expression of B7.1 is downregulated, other co-stimulatory molecules may take over its crucial role to confer protective immune response against M. tuberculosis.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis / immunology
  • B7-1 Antigen / metabolism*
  • B7-2 Antigen / metabolism*
  • Cells, Cultured
  • Coculture Techniques
  • Humans
  • Macrophages / cytology
  • Macrophages / metabolism
  • Macrophages / microbiology*
  • Mycobacterium tuberculosis / immunology*
  • Th1 Cells / cytology*

Substances

  • B7-1 Antigen
  • B7-2 Antigen
  • CD86 protein, human