Hyaluronan binding function of CD44 is transiently activated on T cells during an in vivo immune response.
Though CD44 functions as a cell surface receptor for hyaluronan (HA) in some cell lines, most normal hematopoietic cells expressing CD44 do not bind HA. Certain CD44-specific monoclonal antibodies (mAbs) can rapidly induce CD44-mediated HA binding in normal murine T cells. This observation suggests that in vivo mechanisms may exist for activating the HA receptor function of CD44 on normal T cells. Here, it is shown that up to one third of splenic T cells are capable of CD44-mediated binding of fluorescein-conjugated HA (Fl-HA) during an in vivo allogeneic response. HA binding activity peaks at 7-8 d postinjection and declines rapidly. These rapid kinetics could be the result of transient activation of CD44 function and/or differentiation or expansion of short-lived population(s) that have constitutive HA-binding function. Both CD4 and CD8 T cells are included in the HA binding population which is strongly CD44 positive. After separation of HA-binding cells from nonbinding cells by cell sorting, it is shown that almost all cytotoxic effector cells are found in the HA-binding population. However, there is no evidence that CD44-mediated HA recognition is directly involved in the killing of target cells, since cytotoxicity could not be inhibited by CD44-specific mAbs that inhibit HA binding or by soluble HA. PCR amplification of cDNA reverse transcribed from RNA of sorted HA-binding cells indicated no evidence for CD44 isoforms other than the standard (hematopoietic) form. Though CD44 expression is known to be elevated upon T cell activation, and, as shown here, HA-binding function is induced in a portion of CD44-expressing T cells including cytotoxic effector cells, the role of CD44 and HA-recognition in immune responses is not known.
Lesley
J
J
Department of Cancer Biology, Salk Institute, San Diego, California 92186-5800.
Howes
N
N
Perschl
A
A
Hyman
R
R
D000818:Animals; D002352:Carrier Proteins / Q000502:physiology*; D003602:Cytotoxicity, Immunologic; D018960:Hyaluronan Receptors; D006820:Hyaluronic Acid / Q000378:metabolism*; D008213:Lymphocyte Activation; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D011956:Receptors, Cell Surface / Q000502:physiology*; D016201:Receptors, Lymphocyte Homing / Q000502:physiology*; D013154:Spleen / Q000378:metabolism; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism
D002352:Carrier Proteins; D018960:Hyaluronan Receptors; D011956:Receptors, Cell Surface; D016201:Receptors, Lymphocyte Homing; D006820:Hyaluronic Acid