Development of lntraepithelial Cells in the Porcine Small Intestine
Developmental Immunology
Development of lntraepithelial Cells in the Porcine Small Intestine
M.A. VEGA-L( 0
G. ARENAS-CONTRERAS 0
M. BAILEY 0
S. GONZALEZ-POZOS 0
C.R. STOKES 0
M.G. ORTEGA 0
R. MONDRAG( 0
N-FLORES 0
0 aCenterfor Research and Advanced Studies (CINVESTAV-IPN), Dept. Experimental Pathology
The number, phenotype, localisation and development of intraepithelial lymphocytes (IEL) from duodenum (Du) and ileum (I1) were studied by immunohistochemistry (IHC) and light and electron microscopy in unweaned (0-7 weeks old) and six months-old pigs. Developmental changes at birth showed that 38% of the total lymphocytes in the villi were IEL, mainly of the CD2+CD4-CD8- double negative (DN) phenotype. That proportion rose to over 50% at week 5 after birth, resembling adult proportion, although still with fewer cells than in adult pigs. CD4+ cells appeared relatively early in life although they were confined to the lamina propria (LP) and CD8+ cells were found only in low numbers. In the villi of adult animals, almost'half of the total number of lymphocytes were IEL (49% Du, 52% I1). Over half of these IEL (52% Du, 53% I1) showed the CD2+CD4-CD8+ phenotype and were localized at the epithelium's basement membrane. Numerous (43% Du, 42% I1) DN IEL were found grouped at the enterocyte nucleus level and relatively few (5% in Du and I1) granular IEL were found apically in the epithelium. These proportions were homogeneously maintained along the villi's tip, middle and bottom, suggesting that the IEL may have their origin in the LP. Therefore, the IEL compartment in the porcine intestine develops slowly with age and is actually composed by a heterogeneous population of cells (null, DN and CD8+). These results may explain the increased susceptibility of young animals to disease during the lactation period and should be taken into account when functional studies are carried out with IEL. The quantitative results of this paper established a model for studies on the effect of age, diet, normal flora, infection and oral immunization on the IEL of the gut.
IEL; immune development; lymphocyte; mucosal immunology; small intestine; swine
INTRODUCTION
Oral immunization has aroused great interest and
expectation since this route may represent an
alternative for disease control and also to prevent and control
autoimmune diseases by inducing tolerance to
autologous antigens
(Brandtzaeg, 1995)
. The mucosal
immune system has some similarities but also many
differences with the systemic immune system
(Stokes, 1988; Kiyono, et al., 1992)
. On the one hand,
both systems contain cells which follow similar
developmental pattems and effector functions
(McGhee and Kiyono, 1993). On the other,
differences in cell distribution and immune regulation have
also been described
(Kiyono, et al., 1992)
. Unlike the
systemic immunological tissues, the mucosal immune
system in the gut must continuously deal with an
enormous array of foreign material and must be able
to accurately discriminate between harmless food
antigens and commensal microorganisms and
hazardous material, inducing anergy and/or tolerance to the
former and a strong local and systemic immune
response against the latter
(Bienenstock, et al., 1987;
Moqbel and MacDonald, 1990; Stokes, et al., 1994)
.
Moreover, the local immune system must maintains
an appropriate balance between the organism and
bacteria from the normal flora of the gut by mechanisms
such as IgA-mediated immune exclusion
(Stokes et
al. 1975; Walker, 1987; Husby, 1988; Brandtzaeg,
1995)
. These two functions of the local immune
system are likely to be carried out through regulatory
mechanisms different to those found in the systemic
immune system and, perhaps, through subtle but
substantial differences in the type and function of the
cells found at the mucosal sites.
The gut contains the largest number of immune
cells in the organism, approximately 60% of all
lymphocytes
(Parrot, 1987; Hamad and Klein, 1994;
Takahashi and Kiyono, 1999)
. Many T cells are
located in the lamina propria (LPL) and within the
epithelium (intraepithelial lymphocytes, IEL)
(Moqbel and MacDonald, 1990)
. Because of their
vicinity to the intestinal lumen and their access to
food antigens, IEL are strategically located to induce,
regulate and perform immune responses
(Pabst, 1987;
Cerf-Bensussan and Guy-Grand, 1991; McGhee, et
al., 1992)
. Previous studies in the pig have
demonstrated that, unlike rodents and humans, the lymphoid
components of the intestinal villi are poorly
developed at birth
(Vega-Lopez, et al., 1993; Pabst and
Rothkotter, 1999)
. The postnatal development of this
compartment appears to be driven by exposure to
microbial antigens, since it does not occur in
germ-free pigs
(Pabst and Rothkotter, 1999)
and is
accelerated by weaning in conventional pigs
(Vega-Lopez, et al., 1995)
. The pig therefore provides
an appropriate system to study the development of
IEL compartments in response to antigen. (...truncated)