Postnatal maturation of mast cell subpopulations in the rat respiratory tract.

The distribution and enumeration of mast cell subpopulations within the respiratory tract of a high- and low-Ige responder rat strain was determined during postnatal development. Mast cells were identified in adjacent sections by the alcian blue (AB)/safranin (SAF) staining sequence, or using immunoperoxidase to detect the rat mast cell proteinases I (RMCPI) or II (RMCPII). At birth both mucosal mast cells (MMC) and connective tissue mast cells (CTMC) were represented in very low numbers at distinct locations throughout the respiratory tract. The total number of mast cells increased with age. MMC (AB+/RMCPII+ mast cells) were the predominant phenotype in the epithelium and lamina propria of the trachea and the major conducting airways of the lung in all age groups. In contrast, CTMC (AB+/RPMCPI+ and SAF+/RMCPI+ mast cells) predominated in the submucosa of the trachea and major conducting airways as well as in the parenchyma and visceral pleura of the peripheral lung. Both phenotypes co-exist in similar proportions in peribronchial adventitial tissue and adventitia surrounding large blood vessels in neonates as well as adults. In rats the tracheal epithelium is densely populated by MMC from around the time of weaning (3 weeks) and a small but generalized increase in the number of MMC at all sites within the respiratory tract is noted from this time. This increase in MMC frequency in tissue sections with increasing age is mirrored by the levels of circulating serum RMCPII. The number of bone marrow-derived MMC also increased with increasing age prior to weaning, with a significant drop (P less than 0.01) at 4 weeks of age before returning to the peak numbers in 3-week-old rats. The high-IgE responder Brown Norwegian (BN) rat strain constitutively produces significantly more IgE than the low-IgE responder White albino Glaxo (WAG) strain (P less than 0.001) at all ages studied. In contrast, only minor differences between the number and distribution of mast cells in the two strains were observed.

Specificity of Toxocara ELISA in tropical populations.

The diagnosis of human infection by Toxocara canis relies heavily upon serological tests, the specificity of which can be inadequate in regions of endemic helminthiasis. When different population groups of tropical Venezuela were evaluated using ELISA based upon Toxocara excretory-secretory antigen (TcESA), solid-phase adsorption of the sera with extracts of a wide variety of non-homologous parasites revealed the existence of significant cross-reactivity. This was effectively and conveniently overcome when the test sera were incubated in the presence of the soluble parasite extracts in a competitive inhibition ELISA. The mean reduction of ELISA values caused by pre-adsorption of the sera tested was 32.2%, and that caused by competitive inhibition was 42.3%, the effects of these two procedures being strongly correlated (r = 0.83). The magnitude of the reduction was inversely proportional to the actual ELISA value (r = -0.55), and ranged from a mean of 68.0% in sera from apparently healthy individuals of medium-high socio-economic level, down to 28.1% in heavily parasitized Amazon indians. Ascaris showed the greatest degree of cross-reactivity in these tests, although under conditions of competitive inhibition even sera with high levels of antibody against this parasite could be negative in Toxocara ELISA. Western blotting revealed a major 81,400 D component that was shared between Ascaris and TcESA. Our results indicate that the competitive inhibition of cross-reactivity by soluble non-homologous parasite extracts provides a convenient and economical means of increasing the specificity of ELISA for the determination of the seroprevalence of toxocariasis in tropical populations.