Cellular expression of H and B antigens in the rat olfactory system during development

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Abstract
Developmental expression of H and B antigens in the rat olfactory system was studied from the embryonic day 14 up to the postnatal day 30. The H antigen was detected in the olfactory and vomeronasal epithelia as early as fetal day 14, whereas the B antigen first appeared 2 days later. The anti‐H reagent reacted strongly with sensory receptors and weakly with supporting cells in both epithelia, whereas the anti‐B reagent was specific for olfactory receptors. In the main olfactory epithelium, the H antigen was expressed from fetal day 19 by most of the receptor cells, whereas the B determinant was expressed from fetal day 16 to postnatal day 3 by only a few neuroreceptors mostly located near the epithelial surface. After the postnatal day 3, B positive neurons increased in number from the periphery toward the deeper mucosal layers and they were distributed over 3/4 of the epithelial thickness in 15‐ and 30‐day‐old rats. In the main olfactory bulb, a widespread glomerular B staining with variable binding intensity between adjacent glomeruli was already observed at birth. The vomeronasal receptor cells and their axon terminals in the accessory olfactory bulb exhibited a comparable developmental expression of the B antigen. Results suggest that the B antigen could be regarded as a marker of neuronal maturation of both the olfactory and vomeronasal receptor cells; moreover, its first appearance in the receptor cells might be temporally related to the formation of synapses between receptor axons and deutoneurons in the bulb.